chore: remove Open Food Facts (OFF) integration

- Remove off-service.js and off-service.test.js
- Remove OFF import from server.js
- Simplify /api/products/search to only use CIMA
- Remove 'openfoodfacts' from valid product sources
- Update frontend-mobile Product interface to remove OFF source
- Remove OFF env vars from .env.example
- Add PARAPHARMACY_API_URL to .env.example

OFF was replaced by the new parapharmacy-api microservice.

apps/backend/__tests__/server.test.js

@@ -6,11 +6,6 @@ jest.unstable_mockModule('../cima-service.js', () => ({
   searchOTC: jest.fn(async () => []),
 }))
 
-jest.unstable_mockModule('../off-service.js', () => ({
-  searchBabyProducts: jest.fn(async () => []),
-  getBabyProductDetails: jest.fn(async () => null),
-}))
-
 jest.unstable_mockModule('../farmacias-webhook-import.js', () => ({
   runFarmaciaWebhookImport: jest.fn(async () => ({})),
   DEFAULT_FARMACIAS_WEBHOOK: '',