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/ai-routers.js

@@ -189,6 +189,21 @@ function normalizeModels(model, models) {
   return out;
 }
 
+/**
+ * A known Claude model id that Claude Code should treat the router's own model
+ * names as (its `modelPicker` `behavesAs`, issue #56). Optional; `""` clears it.
+ * The user picks it, never AgentHub: it also sets the context window Claude
+ * Code compacts at, and a router may route a name to a non-Claude model.
+ */
+function normalizeBehavesAs(value) {
+  const clean = typeof value === "string" ? value.trim() : null;
+  if (clean === "") return "";
+  if (!clean || !/^claude-[a-z0-9][a-z0-9.-]{0,99}$/.test(clean)) {
+    throw err("EBADMODEL", "behavesAs must be a Claude model id, e.g. claude-opus-5-5");
+  }
+  return clean;
+}
+
 function assertNotBuiltin(name) {
   if (name === BUILTIN_NAME) {
     throw err("EBUILTIN", `'${BUILTIN_NAME}' is the built-in profile and cannot be changed`);
@@ -250,7 +265,7 @@ function getRouter(name) {
 
 /**
  * @param {{label:string, baseUrl:string, apiKey?:string, model:string,
- *   models?:Record<string,string>}} input
+ *   models?:Record<string,string>, behavesAs?:string}} input
  * @returns the browser-safe view of what was saved
  */
 function createRouter(input = {}) {
@@ -265,6 +280,7 @@ function createRouter(input = {}) {
     apiKey: typeof input.apiKey === "string" ? input.apiKey.trim() : "",
     model,
     models: normalizeModels(model, input.models),
+    behavesAs: input.behavesAs === undefined ? "" : normalizeBehavesAs(input.behavesAs),
     savedAt: new Date().toISOString(),
   };
 
@@ -297,6 +313,10 @@ function updateRouter(name, changes = {}) {
       changes.model === undefined && changes.models === undefined
         ? stored.models
         : normalizeModels(model, changes.models ?? stored.models),
+    behavesAs:
+      changes.behavesAs === undefined
+        ? (stored.behavesAs ?? "")
+        : normalizeBehavesAs(changes.behavesAs),
     savedAt: new Date().toISOString(),
   };