feat(lanes): Add Lane repo/worktree mode toggle, manual branch, folder browse

- Repo mode adopts a directory as-is via /lanes/ensure (no worktree, no
  branch fields) - the right choice for a main repo you want stage
  detection on. Worktree mode (default) keeps the existing provisioning
  flow but now requires a manually-typed branch name instead of deriving
  one from the title.
- POST /lanes/worktree accepts an optional `branch`, validated via
  `git check-ref-format --branch`; omitting it preserves the CLI's
  existing auto-derived-branch behavior.
- New GET /lanes/browse lists a directory's immediate subdirectories,
  backing a small folder-browse modal on both path fields - browsers
  cannot expose an absolute path from a native picker, so this is
  server-backed instead, consistent with the tool's local-first model.

client/src/components/lanes/AddLaneModal.tsx

@@ -1,21 +1,27 @@
 /**
  * @file AddLaneModal.tsx
- * @description The "+ Add lane" flow: pick a SOURCE repo (not a folder to
- * adopt), pick which of its branches to fork from, name the feature, and the
- * dashboard provisions a managed git worktree via `POST /api/lanes/worktree`
- * — the dashboard invents the lane's own directory and branch name, the same
- * way Shipyard's "+ Add lane" never asks a human to name a folder. The lane
- * returned is `status: "provisioning"`: the route answers before the actual
- * `git worktree add` runs, so this component polls `GET /api/lanes/:id`
- * until that finishes before running the auto-setup calls against a cwd
- * that must actually exist on disk first.
+ * @description The "+ Add lane" flow, in one of two modes chosen with a
+ * segmented toggle: "Repo" adopts an existing directory as-is via
+ * `POST /api/lanes/ensure` (no worktree, no branch — the right mode for a
+ * main repo you want stage detection on); "Worktree" provisions a
+ * dashboard-managed git worktree via `POST /api/lanes/worktree` with a
+ * manually-typed branch name. Either mode's path field can be filled by
+ * typing, by the CwdAutocomplete suggestions, or by browsing
+ * (`FolderBrowseModal`) — a native folder picker cannot hand a web page an
+ * absolute filesystem path, so browsing is server-backed instead. The
+ * worktree lane returned is `status: "provisioning"`: the route answers
+ * before the actual `git worktree add` runs, so this component polls
+ * `GET /api/lanes/:id` until that finishes before running the auto-setup
+ * calls against a cwd that must actually exist on disk first.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
 import { useCallback, useEffect, useRef, useState } from "react";
 import { useTranslation } from "react-i18next";
+import { FolderOpen } from "lucide-react";
 import { ConfirmModal } from "../ConfirmModal";
 import { CwdAutocomplete } from "../run/RunSetup";
+import { FolderBrowseModal } from "./FolderBrowseModal";
 import { api } from "../../lib/api";
 import type { CwdSuggestion } from "../../lib/api";
 import type { Lane } from "../../lib/types";
@@ -36,6 +42,33 @@ async function waitForProvisioned(
   }
 }
 
+/** One segment of a two-way inline choice, styled to match RunSetup's `Seg`. */
+function Seg({
+  active,
+  label,
+  title,
+  onClick,
+}: {
+  active: boolean;
+  label: string;
+  title?: string;
+  onClick: () => void;
+}) {
+  return (
+    <button
+      type="button"
+      onClick={onClick}
+      title={title}
+      aria-pressed={active}
+      className={`rounded px-2 py-0.5 text-xs font-medium transition-colors ${
+        active ? "bg-accent/20 text-accent" : "text-fg-secondary hover:text-fg-primary"
+      }`}
+    >
+      {label}
+    </button>
+  );
+}
+
 export function AddLaneModal({
   open,
   onClose,
@@ -44,20 +77,23 @@ export function AddLaneModal({
 }: {
   open: boolean;
   onClose: () => void;
-  /** Called with the newly provisioned (still-provisioning) lane. */
+  /** Called with the newly created (possibly still-provisioning) lane. */
   onAdded: (lane: Lane) => void;
   /** The same suggestion list the Run form already fetched (dashboard cwd,
    *  home, recently-used paths) — reused rather than fetched a second time. */
   cwdSuggestions: CwdSuggestion[];
 }) {
   const { t } = useTranslation(["lanes"]);
+  const [mode, setMode] = useState<"repo" | "worktree">("worktree");
   const [sourceRepo, setSourceRepo] = useState("");
   const [title, setTitle] = useState("");
+  const [branch, setBranch] = useState("");
   const [branches, setBranches] = useState<string[] | null>(null);
   const [base, setBase] = useState("");
   const [branchesError, setBranchesError] = useState<string | null>(null);
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [browseOpen, setBrowseOpen] = useState(false);
   const [setupResult, setSetupResult] = useState<{
     profile: "scaffolded" | "skipped" | "failed";
     agents: "ok" | "failed";
@@ -65,8 +101,10 @@ export function AddLaneModal({
   } | null>(null);
 
   const reset = () => {
+    setMode("worktree");
     setSourceRepo("");
     setTitle("");
+    setBranch("");
     setBranches(null);
     setBase("");
     setBranchesError(null);
@@ -77,9 +115,11 @@ export function AddLaneModal({
 
   // Look up the repo's branches once the path settles - debounced so every
   // keystroke while typing a path doesn't fire a request against a path that
-  // isn't finished yet.
+  // isn't finished yet. Worktree mode only: "Repo" mode adopts as-is and
+  // never forks a branch.
   const lookedUpFor = useRef<string>("");
   useEffect(() => {
+    if (mode !== "worktree") return;
     const path = sourceRepo.trim();
     if (!path) {
       setBranches(null);
@@ -105,19 +145,35 @@ export function AddLaneModal({
       }
     }, 300);
     return () => window.clearTimeout(timer);
-  }, [sourceRepo, t]);
+  }, [mode, sourceRepo, t]);
 
   const submit = async () => {
     const repo = sourceRepo.trim();
     const name = title.trim();
-    if (!repo || !branches || !name) return;
+    if (!repo) return;
     setBusy(true);
     setError(null);
+
+    if (mode === "repo") {
+      try {
+        const result = await api.lanes.ensure({ cwd: repo, title: name || undefined });
+        onAdded(result.lane);
+        reset();
+        onClose();
+      } catch (err) {
+        setError(err instanceof Error ? err.message : String(err));
+        setBusy(false);
+      }
+      return;
+    }
+
+    if (!branches || !name || !branch.trim()) return;
     try {
       const result = await api.lanes.worktree({
         sourceRepo: repo,
         title: name,
         base: base || undefined,
+        branch: branch.trim(),
       });
       onAdded(result.lane);
 
@@ -175,9 +231,21 @@ export function AddLaneModal({
   // into after the very first character. useCallback keeps the identity stable
   // across renders so only mount/unmount (and a real onClose change) refocuses.
   const handleCancel = useCallback(() => {
+    // ConfirmModal's own Escape/backdrop/X handling calls this directly.
+    // While the folder browser is open on top of it, that dismissal should
+    // close only the browser, not both modals at once.
+    if (browseOpen) {
+      setBrowseOpen(false);
+      return;
+    }
     reset();
     onClose();
-  }, [onClose]);
+  }, [onClose, browseOpen]);
+
+  const disabled =
+    !!setupResult ||
+    !sourceRepo.trim() ||
+    (mode === "worktree" && (!title.trim() || !branches || !branch.trim()));
 
   return (
     <ConfirmModal
@@ -187,22 +255,52 @@ export function AddLaneModal({
       cancelLabel={t("destructive.cancel")}
       destructive={false}
       busy={busy}
-      disabled={!!setupResult || !sourceRepo.trim() || !title.trim() || !branches}
+      disabled={disabled}
       onConfirm={submit}
       onCancel={handleCancel}
     >
       <div className="space-y-3">
+        <div className="flex items-center rounded-md border border-border bg-surface-2 p-0.5">
+          <Seg
+            active={mode === "repo"}
+            label={t("mode.repo")}
+            title={t("mode.repoHint")}
+            onClick={() => setMode("repo")}
+          />
+          <Seg
+            active={mode === "worktree"}
+            label={t("mode.worktree")}
+            title={t("mode.worktreeHint")}
+            onClick={() => setMode("worktree")}
+          />
+        </div>
+
         <div>
           <label className="mb-1 block text-xs text-fg-secondary" htmlFor="add-lane-repo">
-            {t("addLaneRepoLabel")}
+            {mode === "repo" ? t("addLaneRepoLabelAdopt") : t("addLaneRepoLabel")}
           </label>
-          <CwdAutocomplete
-            inputId="add-lane-repo"
-            value={sourceRepo}
-            onChange={setSourceRepo}
-            suggestions={cwdSuggestions}
-          />
-          <p className="mt-1 text-[10px] text-fg-muted">{t("addLaneRepoHint")}</p>
+          <div className="flex gap-1.5">
+            <div className="min-w-0 flex-1">
+              <CwdAutocomplete
+                inputId="add-lane-repo"
+                value={sourceRepo}
+                onChange={setSourceRepo}
+                suggestions={cwdSuggestions}
+              />
+            </div>
+            <button
+              type="button"
+              onClick={() => setBrowseOpen(true)}
+              title={t("browse.title")}
+              className="flex items-center gap-1 rounded-md border border-border-light px-2 text-xs text-fg-secondary hover:bg-surface-2"
+            >
+              <FolderOpen className="h-3.5 w-3.5" />
+              {t("browse.button")}
+            </button>
+          </div>
+          <p className="mt-1 text-[10px] text-fg-muted">
+            {mode === "repo" ? t("addLaneRepoHintAdopt") : t("addLaneRepoHint")}
+          </p>
         </div>
 
         <div>
@@ -218,7 +316,7 @@ export function AddLaneModal({
           />
         </div>
 
-        {branches && (
+        {mode === "worktree" && branches && (
           <div>
             <label className="mb-1 block text-xs text-fg-secondary" htmlFor="add-lane-base">
               {t("addLaneBaseLabel")}
@@ -241,10 +339,26 @@ export function AddLaneModal({
             )}
           </div>
         )}
-        {branchesError && !branches && (
+        {mode === "worktree" && branchesError && !branches && (
           <p className="text-[10px] text-status-warning">{branchesError}</p>
         )}
 
+        {mode === "worktree" && branches && (
+          <div>
+            <label className="mb-1 block text-xs text-fg-secondary" htmlFor="add-lane-branch">
+              {t("addLaneBranchLabel")}
+            </label>
+            <input
+              id="add-lane-branch"
+              value={branch}
+              onChange={(e) => setBranch(e.target.value)}
+              placeholder={t("addLaneBranchPlaceholder")}
+              className="w-full rounded-md border border-border-light bg-surface-0 px-3 py-1.5 font-mono text-xs text-fg-primary placeholder:text-fg-muted focus:border-blue-500 focus:outline-none"
+            />
+            <p className="mt-1 text-[10px] text-fg-muted">{t("addLaneBranchHint")}</p>
+          </div>
+        )}
+
         {setupResult && (
           <div className="rounded-md border border-border-light bg-surface-0 p-2 space-y-1">
             <p className="text-[10px] font-medium text-fg-secondary">{t("addLaneSetupTitle")}</p>
@@ -283,6 +397,13 @@ export function AddLaneModal({
           </p>
         )}
       </div>
+
+      <FolderBrowseModal
+        open={browseOpen}
+        initialPath={sourceRepo.trim() || undefined}
+        onSelect={setSourceRepo}
+        onClose={() => setBrowseOpen(false)}
+      />
     </ConfirmModal>
   );
 }