feat: AI commit messages, change tree, router behavesAs, sidebar times (v2.2.0)

- Changes panel: Files and Changes merged into one panel; the overview's
  groups drawn as a folder tree (compacted chains, file counts, fold,
  stage/unstage a whole folder)
- AI-suggested commit message for what is staged
  (POST /api/lanes/:id/git/commit-message, claude -p --safe-mode, haiku)
- AI Router: optional "Behaves as" Claude model id, written as
  modelPicker options into the router's --settings file (issue #56)
- Sidebar: session rows show last activity, live rows their start time;
  a closed Terminal row can be removed (DELETE /api/run/history/:id)
- Every pane's CLI starts only once a client is attached; claude panes
  no longer forced inline; tmux scrollbar one column wide
- Update notifier: "Check for updates" reopens a closed notice

server/lib/tmux.js

@@ -99,13 +99,15 @@ function enableMouse(name) {
     execImpl(["set-option", "-t", pane(name), "pane-scrollbars", "on"]);
     // tmux's default (`fg=white,bg=black,width=1`) is a one-column track in
     // ANSI black — the terminal theme's border colour, almost the background —
-    // so it reads as no scrollbar at all. Two columns, bright slider.
+    // so it reads as no scrollbar at all. Bright slider. ONE column: tmux 3.7c
+    // reserves `width` columns but paints only the first, so a second one is
+    // never cleared and shows stale cells — a ghost second scrollbar.
     execImpl([
       "set-option",
       "-t",
       pane(name),
       "pane-scrollbars-style",
-      "fg=brightwhite,bg=black,width=2,pad=0",
+      "fg=brightwhite,bg=black,width=1,pad=0",
     ]);
   } catch {
     /* tmux < 3.7 */