feat: add barcode scanner with OpenFoodFacts integration

- Camera-based barcode scanning in FoodSearch using barcode-detector (ZXing WASM)
- Import script to load OFF MongoDB dump into lean openfoodfacts collection
  with kJ→kcal fallback and dedup handling
- Barcode lookup API with live OFF API fallback that caches results locally,
  progressively enhancing the local database
- Add 'off' source to food log, custom meal, and favorite ingredient models
- OpenFoodFact mongoose model for the openfoodfacts collection

package.json

@@ -48,8 +48,10 @@
 	"dependencies": {
 		"@auth/sveltekit": "^1.11.1",
 		"@huggingface/transformers": "^4.0.0",
+		"@nicolo-ribaudo/chokidar-2": "2.1.8-no-fsevents.3",
 		"@sveltejs/adapter-node": "^5.0.0",
 		"@tauri-apps/plugin-geolocation": "^2.3.2",
+		"barcode-detector": "^3.1.2",
 		"chart.js": "^4.5.0",
 		"chartjs-adapter-date-fns": "^3.0.0",
 		"date-fns": "^4.1.0",