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/Dockerfile

@@ -1,14 +1,24 @@
 # Node.js backend
 FROM node:18-alpine
 
+# Build tools needed for better-sqlite3 native compilation
+RUN apk add --no-cache python3 make g++
+
 WORKDIR /app
 
 COPY package*.json ./
 
 RUN npm install --omit=dev
 
+# Remove build tools after install to keep image small
+RUN apk del python3 make g++
+
 COPY . .
 
+# Create data directory for SQLite
+RUN mkdir -p /data
+VOLUME /data
+
 EXPOSE 3001
 
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \