feat(lanes,ui): per-lane git surface — Changes panel, VS Code-style diff, branch-aware Add lane, redesigned tooltips (#34, #35)

- Changes card beside lane detail with five modes: Files tree, overview,
  Review (whole diff, per-file collapse), single file, commit history.
- LaneDiffView: unified / side-by-side with independent scroll on both axes
  and mirrored scrollLeft, expand/collapse context, intra-line emphasis.
- Staged-only commit box; git actions (fetch/pull/push/stage/unstage/
  discard/commit/switch/branch-create/branch-delete) guarded in git-ops.js.
- Server: git-diff.js + git-ops.js behind GET /api/lanes/:id/git/* and
  POST /api/lanes/:id/git/:action; gitFacts gains upstream/ahead/behind.
- Add lane: new/existing branch, current branch, worktree list, prefill
  from the git bar's "New lane here"; /api/run/cwds gains a repo kind.
- GlobalTooltip upgrades every native title into a themed anchored bubble;
  chart/info popovers use theme tokens.

client/src/components/lanes/LaneCard.tsx

@@ -24,6 +24,7 @@ import { useCallback, useEffect, useLayoutEffect, useRef, useState } from "react
 import { createPortal } from "react-dom";
 import { useTranslation } from "react-i18next";
 import { DestructiveLaneModal } from "./DestructiveLaneModal";
+import { LaneGitBar } from "./LaneGitBar";
 import { api } from "../../lib/api";
 import { eventBus } from "../../lib/eventBus";
 import { keepIfSame } from "../../lib/keepIfSame";
@@ -49,8 +50,11 @@ const LOCKS_REFRESH_MS = 30_000;
  * polled lane list. Absent facts are not an error state: a lane may point at a
  * plain directory, and it renders as a card without a git row.
  */
-function useLaneGitFacts(laneId: number): LaneGitFacts | null {
+function useLaneGitFacts(laneId: number): [LaneGitFacts | null, () => void] {
   const [facts, setFacts] = useState<LaneGitFacts | null>(null);
+  // Bumped by the git action bar: a commit or a pull changes every fact on
+  // this row, and waiting out the 30s poll makes the button look inert.
+  const [nonce, setNonce] = useState(0);
 
   useEffect(() => {
     let alive = true;
@@ -72,9 +76,9 @@ function useLaneGitFacts(laneId: number): LaneGitFacts | null {
       alive = false;
       clearInterval(timer);
     };
-  }, [laneId]);
+  }, [laneId, nonce]);
 
-  return facts;
+  return [facts, () => setNonce((n) => n + 1)];
 }
 
 /**
@@ -609,6 +613,7 @@ export default function LaneCard({
   onAction,
   childWorktrees,
   onSelectLane,
+  onNewLaneFromRepo,
 }: {
   lane: Lane;
   onAction: (action: string, body?: Record<string, unknown>) => void;
@@ -618,6 +623,9 @@ export default function LaneCard({
   childWorktrees?: Lane[];
   /** Jumps the Workspace page's selection to another lane's card. */
   onSelectLane?: (id: number) => void;
+  /** Opens the Add-lane flow prefilled with this lane's repo, for a sibling
+   *  worktree on `branch`. Omitted where that flow is not reachable. */
+  onNewLaneFromRepo?: (repo: string, branch?: string) => void;
 }) {
   const { t } = useTranslation(["lanes"]);
   const [destructiveAction, setDestructiveAction] = useState<"reset" | null>(null);
@@ -639,7 +647,7 @@ export default function LaneCard({
     filesCloseTimer.current = window.setTimeout(() => setFilesOpen(false), 150);
   }, []);
   useEffect(() => () => window.clearTimeout(filesCloseTimer.current), []);
-  const git = useLaneGitFacts(lane.id);
+  const [git, refreshGit] = useLaneGitFacts(lane.id);
   const runtime = useLaneRuntime(lane.id, runtimeBump);
   const locks = useLaneLocks(lane.slot);
 
@@ -809,6 +817,21 @@ export default function LaneCard({
             )}
           </div>
         )}
+        {git?.available && (
+          <LaneGitBar
+            laneId={lane.id}
+            git={git}
+            onChanged={refreshGit}
+            /* A sibling worktree forks from the lane's SOURCE repo when it
+               has one (this lane is itself a worktree of it); an adopted lane
+               is its own repo. */
+            onNewLane={
+              onNewLaneFromRepo
+                ? (branch) => onNewLaneFromRepo(lane.source_repo || lane.cwd, branch)
+                : undefined
+            }
+          />
+        )}
         {/* The lane's own recorded branch, shown only when git could not be
             read — otherwise it duplicates the live branch above. */}
         {!git?.available && lane.branch && (