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/pages/__tests__/Workspace.test.tsx

@@ -722,4 +722,16 @@ describe("Workspace — home and session view", () => {
     await userEvent.setup().click(screen.getByTestId("workspace-back-home"));
     expect(await screen.findByTestId("workspace-home")).toBeInTheDocument();
   });
+  it("widens one pane to two for &pane=1, so the run opens beside the first", async () => {
+    localStorage.removeItem("agenthub.workspace.splitView");
+    render(
+      <MemoryRouter initialEntries={["/workspace?lane=1&run=agenthub-lane-1&pane=1"]}>
+        <Workspace />
+      </MemoryRouter>
+    );
+    await settle();
+    await settle();
+    expect(screen.getAllByTestId("console-body")).toHaveLength(2);
+    expect(JSON.parse(localStorage.getItem("agenthub.workspace.splitView")!).layout).toBe(2);
+  });
 });