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).

client/src/components/Layout.tsx

@@ -86,6 +86,7 @@ export function Layout({ wsConnected }: LayoutProps) {
   const { t } = useTranslation("nav");
   const [collapsed, setCollapsed] = useState(loadCollapsed);
   const [connectionOpen, setConnectionOpen] = useState(false);
+  const [updateAvailable, setUpdateAvailable] = useState(false);
   const sidebarWidth = collapsed ? "4.25rem" : "15rem";
 
   const toggle = useCallback(() => {
@@ -111,6 +112,7 @@ export function Layout({ wsConnected }: LayoutProps) {
         onToggle={toggle}
         connectionOpen={connectionOpen}
         onConnectionOpenChange={setConnectionOpen}
+        onUpdateAvailableChange={setUpdateAvailable}
       />
       <main
         id="main-content"
@@ -132,6 +134,7 @@ export function Layout({ wsConnected }: LayoutProps) {
         wsConnected={wsConnected}
         left={sidebarWidth}
         onConnectionClick={() => setConnectionOpen(true)}
+        updateAvailable={updateAvailable}
       />
     </div>
   );