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/__tests__/tmux.test.js

@@ -59,7 +59,7 @@ describe("tmux wrapper", () => {
       "-t",
       "=agenthub-lane-1:",
       "pane-scrollbars-style",
-      "fg=brightwhite,bg=black,width=2,pad=0",
+      "fg=brightwhite,bg=black,width=1,pad=0",
     ]);
   });