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/LaneCard.tsx

@@ -100,7 +100,8 @@ function useLaneLocks(laneSlot: number | null): NamedLock[] {
 
 export const LIVENESS_DOT: Record<Lane["liveness"], string> = {
   active: "bg-status-success",
-  idle: "bg-surface-4",
+  // A ring: a surface-4 fill vanished on the light themes.
+  idle: "border border-fg-muted",
   dead: "bg-status-danger",
 };
 
@@ -128,7 +129,6 @@ export default function LaneCard({
 }) {
   const { t } = useTranslation(["lanes"]);
   const [destructiveAction, setDestructiveAction] = useState<"reset" | null>(null);
-  const [menuOpen, setMenuOpen] = useState(false);
   const [menuAt, setMenuAt] = useState<MenuPoint | null>(null);
   const [runtimeBump, setRuntimeBump] = useState(0);
   const [bootLine, setBootLine] = useState<string | null>(null);
@@ -203,9 +203,13 @@ export default function LaneCard({
               <div key={name} className="flex items-center gap-1.5 truncate">
                 <span
                   className={`h-1.5 w-1.5 shrink-0 rounded-full ${
-                    info.listening ? "bg-status-success" : "bg-surface-4"
+                    info.listening ? "bg-status-success" : "border border-fg-muted"
                   }`}
+                  aria-hidden
                 />
+                <span className="sr-only">
+                  {info.listening ? t("runtime.listening") : t("runtime.notListening")}
+                </span>
                 <span className="text-fg-secondary">{name}</span>
                 <span className="text-fg-muted">:{info.port ?? "—"}</span>
                 {info.port !== null && info.port !== info.expected && (
@@ -265,7 +269,7 @@ export default function LaneCard({
                   <button
                     type="button"
                     onClick={() => onSelectLane?.(w.id)}
-                    className="truncate text-left text-blue-700 dark:text-blue-400 hover:underline"
+                    className="truncate text-left text-accent hover:underline"
                     title={w.cwd}
                   >
                     #{w.id} {w.title || w.cwd} · {w.status}
@@ -283,42 +287,23 @@ export default function LaneCard({
             applies to managed lanes and is rare enough to stay behind ⋯. */}
         {lane.kind === "managed" && (
           <div className="mt-auto flex items-center justify-end gap-1 border-t border-border pt-2 text-xs">
-            <div className="relative">
-              <button
-                type="button"
-                data-testid="lane-more"
-                aria-haspopup="menu"
-                aria-expanded={menuOpen}
-                onClick={(e) => {
-                  e.stopPropagation();
-                  setMenuOpen((v) => !v);
-                }}
-                className="rounded px-2 py-1 text-fg-muted hover:bg-surface-2 hover:text-fg-secondary"
-                title={t("moreActions")}
-              >
-                ⋯
-              </button>
-              {menuOpen && (
-                <div
-                  role="menu"
-                  className="absolute right-0 z-10 mt-1 min-w-40 overflow-hidden rounded-md border border-border-light bg-surface-0 py-1 shadow-lg shadow-black/40"
-                >
-                  <button
-                    type="button"
-                    role="menuitem"
-                    data-testid="lane-action-reset"
-                    onClick={(e) => {
-                      e.stopPropagation();
-                      setMenuOpen(false);
-                      setDestructiveAction("reset");
-                    }}
-                    className="block w-full px-3 py-1.5 text-left text-status-warning hover:bg-status-warning/10"
-                  >
-                    {t("action.reset")}
-                  </button>
-                </div>
-              )}
-            </div>
+            {/* The shared menu shell: outside click, Escape and focus. */}
+            <button
+              type="button"
+              data-testid="lane-more"
+              aria-haspopup="menu"
+              aria-expanded={!!menuAt}
+              aria-label={t("moreActions")}
+              onClick={(e) => {
+                e.stopPropagation();
+                const r = e.currentTarget.getBoundingClientRect();
+                setMenuAt(menuAt ? null : { x: r.right - 160, y: r.bottom + 4 });
+              }}
+              className="rounded px-2 py-1 text-fg-muted hover:bg-surface-2 hover:text-fg-secondary"
+              title={t("moreActions")}
+            >
+              ⋯
+            </button>
           </div>
         )}
       </div>
@@ -327,6 +312,7 @@ export default function LaneCard({
         <ContextMenu x={menuAt.x} y={menuAt.y} onClose={() => setMenuAt(null)}>
           <MenuItem
             danger
+            testId="lane-action-reset"
             onSelect={() => {
               setMenuAt(null);
               setDestructiveAction("reset");