feat(workspace): no double resume, server-picked tabs, terminal a11y

- A resume of a session a live pane already holds is refused (409
  ESESSIONLIVE with error.run_id) and the client opens that pane, pasting
  any typed message there; catalog tools refuse resumeSessionId
  (EUNSUPPORTED) instead of silently starting fresh.
- POST /api/lanes/:id/start takes slot: "auto": the server picks the free
  tab under the lane lock (components/lanes/startSession.ts on the client,
  kept out of WorkspaceHome so the sidebar does not pull react-markdown
  into the main bundle).
- Unsaved whole-file edits are guarded on every exit (Back, another file,
  tab switch, close, lane/session change, beforeunload).
- Closing an AI tab asks first; hiding a pane has its own icon. Tabs and
  pane headers show the session name, a state dot, rename by double-click.
- Terminal: Ctrl+M toggles Tab-moves-focus (no keyboard trap), Cmd+F /
  Ctrl+Shift+F find bar, clickable links (noopener), a write-only OSC 52
  clipboard, a Reconnecting overlay, debounced resizes, optional screen
  reader mode. Alt+1-4 / Alt+\ / Alt+W focus, split and hide panes.
- Changes panel: draggable splitter, wrapping git bar, history paging,
  disarming discard/undo/abort, inline diff comments pasted only into a
  visible pane; drag MIME guard on sidebar rows; IME-safe Enter; Show
  more in the sidebar and Recents; idle dots readable with sr-only text.
- Adds @xterm/addon-clipboard, @xterm/addon-search, @xterm/addon-web-links.

client/src/components/lanes/FolderBrowseModal.tsx

@@ -8,10 +8,11 @@
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
-import { useEffect, useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { FolderOpen, FolderGit2, ArrowUp } from "lucide-react";
 import { api } from "../../lib/api";
+import { useDialog } from "../../hooks/useDialog";
 
 export function FolderBrowseModal({
   open,
@@ -45,14 +46,10 @@ export function FolderBrowseModal({
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [open]);
 
-  useEffect(() => {
-    if (!open) return;
-    const onKey = (e: KeyboardEvent) => {
-      if (e.key === "Escape") onClose();
-    };
-    document.addEventListener("keydown", onKey);
-    return () => document.removeEventListener("keydown", onKey);
-  }, [open, onClose]);
+  // The shared dialog contract: focus in, Tab trapped, Escape closes (only
+  // this one when it sits over the Add-workspace modal), focus restored.
+  const panel = useRef<HTMLDivElement>(null);
+  useDialog(open, panel, onClose);
 
   if (!open) return null;
 
@@ -63,6 +60,7 @@ export function FolderBrowseModal({
       role="presentation"
     >
       <div
+        ref={panel}
         className="relative flex max-h-[70vh] w-full max-w-md flex-col rounded-xl border border-border bg-surface-1 shadow-xl shadow-black/40"
         onClick={(e) => e.stopPropagation()}
         role="dialog"
@@ -99,7 +97,7 @@ export function FolderBrowseModal({
               className="flex w-full items-center gap-2 rounded px-2 py-1.5 text-left text-xs text-fg-primary hover:bg-surface-2"
             >
               {entry.isGitRepo ? (
-                <FolderGit2 className="h-3.5 w-3.5 text-blue-700 dark:text-blue-400" />
+                <FolderGit2 className="h-3.5 w-3.5 text-accent" />
               ) : (
                 <FolderOpen className="h-3.5 w-3.5 text-fg-muted" />
               )}