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/lib/changeTree.ts

@@ -0,0 +1,51 @@
+/**
+ * @file Folds the Changes panel's flat list of changed files into a folder
+ * tree, JetBrains' commit-view shape: folders first, then files, each sorted
+ * by name, and a chain of folders that hold nothing but one sub-folder drawn
+ * as ONE row (`src/lib`), so a deep path does not cost a row per level.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+export interface ChangeTreeDir<T> {
+  /** The row's label — one segment, or several joined by `/` when compacted. */
+  name: string;
+  /** The folder's repo-relative path ("" for the root). */
+  path: string;
+  dirs: ChangeTreeDir<T>[];
+  files: { name: string; file: T }[];
+  /** Every file anywhere below. */
+  count: number;
+}
+
+export function changeTree<T extends { path: string }>(rows: T[]): ChangeTreeDir<T> {
+  const root: ChangeTreeDir<T> = { name: "", path: "", dirs: [], files: [], count: 0 };
+  for (const file of rows) {
+    const parts = file.path.split("/");
+    let dir = root;
+    dir.count++;
+    for (const seg of parts.slice(0, -1)) {
+      const path = dir.path ? `${dir.path}/${seg}` : seg;
+      let next = dir.dirs.find((d) => d.path === path);
+      if (!next) dir.dirs.push((next = { name: seg, path, dirs: [], files: [], count: 0 }));
+      next.count++;
+      dir = next;
+    }
+    dir.files.push({ name: parts[parts.length - 1] ?? file.path, file });
+  }
+  const finish = (d: ChangeTreeDir<T>): ChangeTreeDir<T> => {
+    // Never the root: its children are the group's top level.
+    let only: ChangeTreeDir<T> | undefined;
+    while (d.path && d.files.length === 0 && d.dirs.length === 1 && (only = d.dirs[0])) {
+      d = { ...only, name: `${d.name}/${only.name}` };
+    }
+    d.dirs = d.dirs.map(finish).sort((a, b) => a.name.localeCompare(b.name));
+    d.files.sort((a, b) => a.name.localeCompare(b.name));
+    return d;
+  };
+  return finish(root);
+}
+
+/** Every file under a folder, for its stage/unstage-all button. */
+export function treeFiles<T>(d: ChangeTreeDir<T>): T[] {
+  return [...d.files.map((f) => f.file), ...d.dirs.flatMap(treeFiles)];
+}