refactor(vector-sync): clear SonarCloud gate + round-2 nits

Quality-gate fixes (new-code conditions on PR #902):
- new_security_hotspots_reviewed: drop the fake "http://nextcloud" host in the
  manager tests to https:// (python:S5332 ×2).
- new_security_rating: generate the integration test's fake app password with
  secrets.token_urlsafe instead of a hardcoded literal (python:S2068).
- new_reliability_rating: restructure the user_manager sleep so an explicit
  await checkpoint lives inside the cancellation scope — await one waiter
  directly while watching shutdown via start_soon (python:S7490). Behaviour is
  unchanged: timeout, shutdown, or a provisioning ring all end the sleep.

Review nits:
- Move the shutdown test's fail_after(2) to wrap the whole task group so it
  actually bounds the task-group exit (was guarding a no-op sleep); drop the
  sleep(0) stub (python:S7491).
- Type _wake_on's wait_fn as Callable[[], Awaitable[object]].
- Note in _wire_vector_sync_state why provision_signal is set on the singleton
  only, not fanned out to app.state.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/app.py

@@ -397,6 +397,10 @@ def _wire_vector_sync_state(
     ``eviction_task_group`` is deliberately not set here: it only exists once the
     lifespan has entered its ``anyio.create_task_group()`` (after this call), so
     the lifespan assigns it on the singleton directly at that point.
+    ``provision_signal`` is likewise excluded on purpose — only ``user_manager_task``
+    consumes it (request handlers reach it via ``notify_user_provisioned``), so the
+    multi-user lifespan sets it on the singleton directly rather than fanning it out
+    to ``app.state``/the browser sub-app.
     """
     send_stream = transport.send_stream
     receive_stream = transport.receive_stream