feat(ui): sidebar project tree, status bar and a tabbed workbench for workspaces

The Workspace page's lane strip moves into the sidebar as a project tree:
workspaces grouped by git repository (new GET /api/projects, cached in
memory, POST /api/projects/refresh), untracked worktrees with Adopt, inline
rename, drag/Alt+arrow ordering and a right-click row menu. The selected
workspace is the URL's ?lane=, one shared lane list feeds the tree, the new
bottom status bar and the page. The Changes panel gains an activity bar
(Files / Changes / Sessions, with resume), and split panes get a header.

client/src/components/run/__tests__/LaneConsolePane.test.tsx

@@ -483,4 +483,47 @@ describe("LaneConsolePane", () => {
       expect(screen.queryByText("shown")).toBeNull();
     });
   });
+
+  it("resumes a session handed over by the Sessions tab, once per request", async () => {
+    (api.lanes.action as ReturnType<typeof vi.fn>).mockResolvedValue({ run_id: "agenthub-lane-1" });
+    (api.run.get as ReturnType<typeof vi.fn>).mockResolvedValue({
+      id: "agenthub-lane-1",
+      laneId: 1,
+      status: "running",
+      cwd: "/workspace/a",
+      model: null,
+      permissionMode: null,
+      effort: null,
+      resumeSessionId: "s-1",
+      sessionId: null,
+      startedAt: null,
+      promptPreview: null,
+    });
+    const request = { sessionId: "s-1", model: "claude-opus-5-5", nonce: 1 };
+    const { rerender } = render(
+      <MemoryRouter>
+        <LaneConsolePane {...baseProps()} resumeRequest={request} />
+      </MemoryRouter>
+    );
+    await waitFor(() =>
+      expect(api.lanes.action).toHaveBeenCalledWith(
+        1,
+        "start",
+        expect.objectContaining({
+          slot: 0,
+          prompt: "",
+          resumeSessionId: "s-1",
+          model: "claude-opus-5-5",
+        })
+      )
+    );
+    // A re-render with the same request is not a second resume.
+    rerender(
+      <MemoryRouter>
+        <LaneConsolePane {...baseProps()} resumeRequest={{ ...request }} />
+      </MemoryRouter>
+    );
+    await screen.findByTestId("terminal-view");
+    expect(api.lanes.action).toHaveBeenCalledTimes(1);
+  });
 });