feat: workspaces own their sessions; desktop parity; sidebar and settings cleanup

Workspace sessions (docs/plans/desktop-parity, phases 1-5 and 7):
- sessions.lane_id: a workspace lists only the sessions its panes held,
  stamped by bindRunSession (first writer wins, nested `claude -p`
  excluded); GET /api/sessions?lane=&archived=
- session row state dot, double-click rename, archive (sessions.archived_at,
  hides only); the activity bar's duplicate Sessions tab removed
- Fork beside Resume (--fork-session, Claude only), Ctrl/Cmd+click a live
  session opens it in a second pane, a diff line's comment is pasted into
  the workspace's last-focused pane (lib/panePaste.ts)

dashboard_runs stability:
- a pane's previous run is archived as <pane>@<started_at> instead of being
  overwritten by INSERT OR REPLACE
- a run is flagged abandoned only once its tmux session is gone, at boot and
  on the run-heal beat (panes outlive a server restart)

UI:
- sidebar: no footer, language or theme block; small collapse button in the
  brand corner; version + update check in the connection details modal, a
  status-bar dot while a release is out; language in Settings -> General
- one Switch component for every switch, the themed Checkbox for every
  checkbox (no native checkboxes)

Also: AI Tools catalog trimmed to 10 built-ins (custom-file prompt modes
tested through fixtures), and the workspace plans under docs/plans/ (the
multi-user server plan lives in the AgentHub-Server repo).

server/db.js

@@ -1142,6 +1142,35 @@ try {
   db.prepare("ALTER TABLE sessions ADD COLUMN tool TEXT NOT NULL DEFAULT 'claude'").run();
 }
 
+// Migrate: add `lane_id` to sessions — the workspace that OWNS a session: the
+// lane whose dashboard pane held it (stamped by bindRunSession in
+// routes/hooks.js from the hook's run_id) or one the user added it to. Null =
+// a session no workspace started (a terminal, an import). No FK: removing a
+// lane leaves its sessions, which are the user's history. The backfill takes
+// only what dashboard_runs still records — older history is not guessed.
+try {
+  db.prepare("SELECT lane_id FROM sessions LIMIT 1").get();
+} catch {
+  db.prepare("ALTER TABLE sessions ADD COLUMN lane_id INTEGER").run();
+  db.prepare(
+    `UPDATE sessions SET lane_id = (
+       SELECT r.lane_id FROM dashboard_runs r
+       WHERE r.session_id = sessions.id AND r.lane_id IS NOT NULL
+       ORDER BY r.started_at DESC LIMIT 1)
+     WHERE lane_id IS NULL`
+  ).run();
+}
+db.exec(`CREATE INDEX IF NOT EXISTS idx_sessions_lane ON sessions(lane_id)`);
+
+// Migrate: add `archived_at` to sessions — a session the user archived out of
+// its workspace's lists (Claude Desktop's archive). Hides only; nothing about
+// the session, its transcript or its tokens is deleted.
+try {
+  db.prepare("SELECT archived_at FROM sessions LIMIT 1").get();
+} catch {
+  db.prepare("ALTER TABLE sessions ADD COLUMN archived_at TEXT").run();
+}
+
 // How far each Codex rollout journal has been read (server/lib/codex-usage.js).
 // In the DB, not a side file, so a session the user deleted stays deleted
 // until Codex writes to its journal again, while a wiped DB re-imports all.
@@ -1444,6 +1473,8 @@ const stmts = {
   updateSession: db.prepare(
     "UPDATE sessions SET name = COALESCE(?, name), status = COALESCE(?, status), ended_at = COALESCE(?, ended_at), metadata = COALESCE(?, metadata), updated_at = strftime('%Y-%m-%dT%H:%M:%fZ', 'now') WHERE id = ?"
   ),
+  // First writer wins: a session a workspace already owns keeps its owner.
+  claimSessionLane: db.prepare("UPDATE sessions SET lane_id = ? WHERE id = ? AND lane_id IS NULL"),
   reactivateSession: db.prepare(
     "UPDATE sessions SET status = 'active', ended_at = NULL, updated_at = strftime('%Y-%m-%dT%H:%M:%fZ', 'now') WHERE id = ?"
   ),