Fix DB auth: custom Dockerfile bakes trust auth into postgres image

Coolify strips environment variables from image-only services,
so POSTGRES_HOST_AUTH_METHOD=trust never reached the container.
Solution: build a custom DB image with trust auth baked in via
Dockerfile ENV + init script that rewrites pg_hba.conf.

docker-compose.yml

@@ -34,12 +34,8 @@ services:
       start_period: 30s
 
   db:
-    image: postgres:16-alpine
+    build: ./db
     restart: unless-stopped
-    environment:
-      - POSTGRES_USER=fitness
-      - POSTGRES_DB=fitness_rewards
-      - POSTGRES_HOST_AUTH_METHOD=trust
     volumes:
       - fitness_db_data:/var/lib/postgresql/data
     healthcheck: