fix: Docker multi-stage build for sqlite3, health endpoint, productValidator exports

- Dockerfile: multi-stage build (builder with python3+g++ for native addons)
- Dockerfile: wireguard-tools from edge/community repo
- Dockerfile: removed USER appuser (start.sh needs root for wg-quick)
- Dockerfile: health check on port 3000
- Added /health HTTP endpoint in index.js for Docker healthcheck
- Fixed productValidator.js: added named exports (validateProductName, validateProductPrice)
- Added better-sqlite3 as fallback dependency

package.json

@@ -9,6 +9,7 @@
   "dependencies": {
     "archiver": "^7.0.1",
     "axios": "^1.7.7",
+    "better-sqlite3": "^11.10.0",
     "bip39": "^3.1.0",
     "bitcoinjs-lib": "^6.1.6",
     "csv-writer": "^1.6.0",