feat(maestro): debounce the gitroot probe in the spawn form

Typing in the raw cwd field fired one /api/gitroot request per
keystroke (#74). Every keystroke now resets a 250ms window shared with
the TUI draft (GITROOT_PROBE_DEBOUNCE_MS there); probeToken still owns
ordering so a late answer can't overwrite a newer input.

web/src/spawnFormWorktree.test.ts

@@ -132,11 +132,13 @@ describe("spawnForm worktree defaults and branch picker (#61)", () => {
   it("still probes the gitroot for a free-text directory", async () => {
     const form = await mount();
 
-    // Escape hatch: switch to a free-text dir; only now does /api/gitroot fire.
+    // Escape hatch: switch to a free-text dir; only now does /api/gitroot
+    // fire — debounced, so the quiet period must elapse first (#74).
     form.querySelector<HTMLElement>(".project-row.project-other")!.click();
     const raw = form.querySelector<HTMLInputElement>("input[name=cwd_raw]")!;
     raw.value = "/opt/somewhere";
     raw.dispatchEvent(new Event("input"));
+    await vi.advanceTimersByTimeAsync(250);
     await drain();
 
     expect(urls.some((u) => u.includes("/api/gitroot"))).toBe(true);