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/elicitation.py

@@ -70,7 +70,9 @@ async def present_login_url(
             logger.info("User cancelled login flow")
             return "cancelled"
 
-    except Exception as e:
-        # Elicitation not supported by this client - fall back to message
-        logger.debug(f"Elicitation not available ({e}), returning URL in message")
+    except (AttributeError, NotImplementedError) as e:
+        # Elicitation not supported by this client/SDK - fall back to message
+        logger.debug(
+            f"Elicitation not available ({type(e).__name__}: {e}), returning URL in message"
+        )
         return "message_only"