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

web/docker-compose.yml

@@ -3,6 +3,8 @@ services:
     build: ./server
     networks:
       - inventory-network
+    volumes:
+      - server-data:/data
     restart: unless-stopped
     healthcheck:
       test: ["CMD", "node", "-e", "require('http').get('http://localhost:3001/api/health',r=>{process.exit(r.statusCode===200?0:1)}).on('error',()=>process.exit(1))"]
@@ -25,3 +27,6 @@ services:
 networks:
   inventory-network:
     driver: bridge
+
+volumes:
+  server-data: