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/__tests__/Sidebar.theme.test.tsx

@@ -13,7 +13,13 @@ import { Sidebar } from "../Sidebar";
 function renderSidebar(collapsed = false) {
   return render(
     <MemoryRouter>
-      <Sidebar wsConnected collapsed={collapsed} onToggle={() => {}} />
+      <Sidebar
+        wsConnected
+        collapsed={collapsed}
+        onToggle={() => {}}
+        connectionOpen={false}
+        onConnectionOpenChange={() => {}}
+      />
     </MemoryRouter>
   );
 }