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>

nextcloud_mcp_server/auth/login_flow.py

@@ -62,9 +62,10 @@ class LoginFlowV2Client:
     async def initiate(
         self, user_agent: str = "nextcloud-mcp-server"
     ) -> LoginFlowInitResponse:
-        """Initiate Login Flow v2.
+        """Initiate Login Flow v2 by sending an HTTP POST to the Nextcloud instance.
 
-        Posts to /index.php/login/v2 to start a new login flow.
+        Makes an outbound HTTP request to POST /index.php/login/v2 on the
+        configured Nextcloud server to start a new login flow.
 
         Args:
             user_agent: User-Agent string for the app password name
@@ -99,9 +100,10 @@ class LoginFlowV2Client:
         return result
 
     async def poll(self, poll_endpoint: str, poll_token: str) -> LoginFlowPollResult:
-        """Poll for Login Flow v2 completion.
+        """Poll for Login Flow v2 completion by sending an HTTP POST to the Nextcloud instance.
 
-        Posts to the poll endpoint with the token. Nextcloud returns:
+        Makes an outbound HTTP request to the poll endpoint provided by the
+        initiate response. Nextcloud returns:
         - 200 with credentials when the user completes login
         - 404 when still pending
         - Other errors for expired/invalid flows