fix: address PR #589 review findings

- Fix anyio.Lock() created at module import time; use lazy init in
  get_shared_storage() to avoid instantiation before event loop exists
- Stop get_login_flow_session from silently swallowing DB exceptions;
  re-raise and handle in caller with proper error response
- Update ProvisionAccessResponse and UpdateScopesResponse status field
  docs to include all actual values (declined, cancelled, unchanged)
- Narrow except clause in present_login_url to (AttributeError,
  NotImplementedError) instead of bare Exception
- Add KeyError handling in LoginFlowV2Client.initiate() and poll() for
  clear errors on malformed Nextcloud responses
- Simplify redundant env-var bypass branches in scope_authorization.py
- Extract _maybe_login_flow_cleanup() context manager to replace 4
  inline cleanup loop registrations in app.py; move sleep to end of
  loop body so cleanup runs once at startup
- Replace fragile string replacement in _rewrite_login_flow_url with
  proper urllib.parse URL handling

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

nextcloud_mcp_server/auth/scope_authorization.py

@@ -128,20 +128,17 @@ def require_scopes(*required_scopes: str):
             )
 
             if access_token is None:
-                # Check if single-user BasicAuth mode (env var app password)
-                # If NEXTCLOUD_APP_PASSWORD or NEXTCLOUD_PASSWORD is set, bypass scope checks
+                # No OAuth token — either BasicAuth with env var credentials
+                # or BasicAuth without explicit credentials. Both bypass scope checks.
                 settings = get_settings()
                 if settings.nextcloud_app_password or settings.nextcloud_password:
                     logger.debug(
                         f"No access token for {func_name} - allowing (env var app password)"
                     )
-                    return await func(*args, **kwargs)
-
-                # Not in OAuth mode (BasicAuth or no auth)
-                # In BasicAuth mode, all operations are allowed
-                logger.debug(
-                    f"No access token present for {func_name} - allowing (BasicAuth mode)"
-                )
+                else:
+                    logger.debug(
+                        f"No access token present for {func_name} - allowing (BasicAuth mode)"
+                    )
                 return await func(*args, **kwargs)
 
             # ── Login Flow v2: Check stored app password scopes ──