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

client/src/i18n/locales/en/settings.json

@@ -587,6 +587,8 @@
     "fieldApiKeyKeep": "Leave blank to keep the saved key.",
     "fieldModel": "Model",
     "fieldModelHint": "Used for every tier unless you override one below. Many routers accept one symbolic name.",
+    "fieldBehavesAs": "Behaves as (Claude Code)",
+    "fieldBehavesAsHint": "Optional. The Claude model id Claude Code should treat this router's model names as (effort defaults, context window), e.g. claude-opus-5-5. Fill it in when Claude Code says a model isn't described by its model catalog, and name the model the router really sends to. While set, it replaces your own modelPicker setting in these sessions.",
     "perTier": "Per-tier overrides",
     "perTierHint": "Leave a field blank to use the model above.",
     "tier": {