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/search/context.py

@@ -665,6 +665,9 @@ async def _fetch_document_text(
                     logger.warning(f"Deck card {doc_id} not found in any board/stack")
                     return None
 
+            # Type narrowing: card is set if we reach here
+            assert card is not None
+
             # Reconstruct full content as indexed: title + "\n\n" + description
             # This ensures chunk offsets align with indexed content structure
             content_parts = [card.title]