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/client/webdav.py

@@ -1180,9 +1180,11 @@ class WebDAVClient(BaseNextcloudClient):
                     "name": display_name_elem.text,
                     "userVisible": user_visible_elem.text.lower() == "true"
                     if user_visible_elem is not None
+                    and user_visible_elem.text is not None
                     else True,
                     "userAssignable": user_assignable_elem.text.lower() == "true"
                     if user_assignable_elem is not None
+                    and user_assignable_elem.text is not None
                     else True,
                 }
                 logger.debug(f"Found tag '{tag_name}' with ID {tag_info['id']}")