fix: address PR #589 review feedback (round 2)

Consolidate three independent RefreshTokenStorage lazy singletons into a
single lock-protected get_shared_storage() function, eliminating race
conditions on concurrent first-access. Remove blanket try/except in
_get_stored_scopes so storage errors propagate as proper MCP errors
instead of silently triggering "please provision" messages. Handle
declined/cancelled elicitation results in Login Flow tools by cleaning up
sessions and returning clear status. Add update_app_password_scopes() to
avoid unnecessary decrypt/re-encrypt when only scopes change. Add
unprovisioned-user early exit and no-op detection to nc_auth_update_scopes.
Remove four dead config fields and misleading NEXTCLOUD_PASSWORD deprecation
warning. Add periodic login flow session cleanup task. Generate separate
Fernet keys per service. Add board cleanup in deck integration test. Gate
CI unit tests on linting and skip Astrolabe build for single-user profile.
Fix test markers from oauth to multi_user_basic for astrolabe integration
tests. Update login_flow.py docstrings to document outbound HTTP calls.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/integration/test_astrolabe_multi_user_background_sync.py

@@ -27,7 +27,7 @@ from playwright.async_api import Page
 
 logger = logging.getLogger(__name__)
 
-pytestmark = [pytest.mark.integration, pytest.mark.oauth]
+pytestmark = [pytest.mark.integration, pytest.mark.multi_user_basic]
 
 
 async def login_to_nextcloud(page: Page, username: str, password: str):
@@ -899,7 +899,7 @@ def clear_stale_test_state(clear_preferences: bool = False) -> None:
 
 
 @pytest.mark.integration
-@pytest.mark.oauth
+@pytest.mark.multi_user_basic
 async def test_multi_user_astrolabe_background_sync_enablement(
     browser,
     nc_client,
@@ -1246,7 +1246,7 @@ async def verify_app_password_deleted(username: str) -> bool:
 
 
 @pytest.mark.integration
-@pytest.mark.oauth
+@pytest.mark.multi_user_basic
 async def test_revoke_background_sync_access(
     browser,
     nc_client,