fix(deploy): APP_ENV esplicito nei compose (#33)

docker-compose.yml (produzione) non impostava APP_ENV: la guardia
_refuse_default_secrets_outside_dev in src/backend/config.py non
scattava mai perché il default è "dev". Aggiunto APP_ENV: production
al servizio server; docker-compose.dev.yml imposta APP_ENV: dev in
modo esplicito. Tabella env in docs/DEPLOYMENT.md aggiornata.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -31,6 +31,7 @@ services:
     env_file:
       - .env
     environment:
+      APP_ENV: dev
       DB_HOST: mysql
       UPLOAD_DIR: uploads
       VISION_WORKER_URL: http://vision:8100