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/pages/__tests__/Workspace.laneRouter.test.tsx

@@ -11,7 +11,7 @@
 
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { render, act, screen, waitFor } from "@testing-library/react";
-import { MemoryRouter } from "react-router-dom";
+import { MemoryRouter, useSearchParams } from "react-router-dom";
 import userEvent from "@testing-library/user-event";
 
 type LaneFixture = {
@@ -179,9 +179,24 @@ beforeEach(() => {
   h.lanes = lanesToReturn as unknown as typeof h.lanes;
 });
 
+/** Stands in for the sidebar's project tree: picking a workspace sets `?lane=`. */
+function Picker() {
+  const [, setParams] = useSearchParams();
+  return (
+    <>
+      {lanesToReturn.map((l) => (
+        <button key={l.id} onClick={() => setParams({ lane: String(l.id) })}>
+          {`pick ${l.title}`}
+        </button>
+      ))}
+    </>
+  );
+}
+
 async function renderWorkspace() {
   const utils = render(
     <MemoryRouter initialEntries={["/run"]}>
+      <Picker />
       <Workspace />
     </MemoryRouter>
   );
@@ -191,11 +206,9 @@ async function renderWorkspace() {
   return utils;
 }
 
-/** Click the strip tile for a lane, which is how a lane is selected. */
+/** Pick a lane the way the sidebar does: by naming it in the URL. */
 async function selectLane(user: ReturnType<typeof userEvent.setup>, title: string) {
-  const tile = screen.getAllByText(title)[0];
-  if (!tile) throw new Error(`no strip tile for ${title}`);
-  await user.click(tile);
+  await user.click(screen.getByRole("button", { name: `pick ${title}` }));
   await settle();
 }