fix: resolve type checking warnings for CI

- Add type casts for Starlette app state access
- Add assertions for cipher, card, board, stack after initialization
- Add None checks for XML element text attributes
- Handle __package__ being None in tracing setup
- Fix TokenBrokerService initialization to use storage credentials

Resolves 42 type warnings from ty-check, enabling CI linting to pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

nextcloud_mcp_server/vector/processor.py

@@ -379,6 +379,11 @@ async def _index_document(
                         f"Deck card {doc_task.doc_id} not found in any board/stack"
                     )
 
+            # Type narrowing: card, board, stack are all set if we reach here
+            assert card is not None
+            assert board is not None
+            assert stack is not None
+
             # Build content from card title and description
             content_parts = [card.title]
             if card.description: