New Features:
- Added "SQLite Materials Inspector" to the Window menu — a read-only multi-tab viewer for summary stats, brushes by type, and tilesets with reload and detail panes.
- Background initialization and async bootstrap/import of the materials database to avoid blocking the UI; startup/shutdown now synchronize to prevent concurrent access.
Chores:
- New runtime option to enable the SQLite materials backend and control migration/bootstrap behavior (default enabled).
