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/server/package.json

@@ -9,6 +9,7 @@
     "dev": "nodemon server.js"
   },
   "dependencies": {
+    "better-sqlite3": "^11.7.0",
     "cors": "^2.8.5",
     "express": "^4.18.2",
     "ws": "^8.14.2"