Add SQLite persistence + official Minecraft item icons
Database (better-sqlite3):
- Persist items, furnaces, alerts, recipes, settings to SQLite
- Auto-restore last known state when server restarts or bridge disconnects
- Item count history tracking (5-min snapshots, 7-day retention)
- /api/history/:itemName endpoint for item count history
- Docker volume for database file persistence
- Graceful shutdown with DB connection cleanup
Icons:
- Replace mc-heads.net with official Minecraft game textures via CDN
- Cascading fallback: item texture -> block texture -> emoji
- In-memory URL cache to avoid redundant network requests
- Block texture suffix mapping (furnace_front, barrel_top, etc.)
- Crisp pixel-art rendering with image-rendering: pixelated
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