feat(api_hooks): add /api/project_switch_status endpoint for deterministic test signaling

Adds a new endpoint that exposes the project-switch state machine so tests
can poll for completion instead of guessing with timeouts.

- AppController: track _project_switch_error on failure paths
- src/api_hooks.py: GET /api/project_switch_status returns
  {in_progress, pending_path, active_path, error}
- src/api_hook_client.py: get_project_switch_status() helper
- tests/test_api_hooks_project_switch.py: 3 unit tests for client + endpoint
  shape, 1 live_gui test for the default-idle case

src/api_hooks.py

@@ -114,6 +114,26 @@ class HookHandler(BaseHTTPRequestHandler):
     self.end_headers()
     flat = project_manager.flat_config(_get_app_attr(app, "project"))
     self.wfile.write(json.dumps({"project": flat}).encode("utf-8"))
+   elif self.path == "/api/project_switch_status":
+    # Determinstic signal for tests waiting on a project switch to complete.
+    # Polling /api/project returns derived state that may be stale from prior
+    # tests; this endpoint tracks in_progress/error explicitly.
+    # in_progress: True while _do_project_switch is scheduled or running
+    # path: target path (or last completed path)
+    # error: string error if last switch failed; None on success/idle
+    self.send_response(200)
+    self.send_header("Content-Type", "application/json")
+    self.end_headers()
+    controller = _get_app_attr(app, "controller", None)
+    if controller is None:
+     payload = {"in_progress": False, "path": None, "error": None}
+    else:
+     payload = {
+      "in_progress": bool(getattr(controller, "_project_switch_in_progress", False)),
+      "path": getattr(controller, "_project_switch_pending_path", None) or getattr(controller, "active_project_path", None),
+      "error": getattr(controller, "_project_switch_error", None),
+     }
+    self.wfile.write(json.dumps(payload).encode("utf-8"))
    elif self.path == "/api/session":
     self.send_response(200)
     self.send_header("Content-Type", "application/json")