fix: move cache:warmup to runtime entrypoint, fix POSTGRES_PASSWORD default

cache:warmup at build time fails because .env.local is not available in the
image (gitignored). Moved to entrypoint.sh which runs after volume mounts.
Also added default value for POSTGRES_PASSWORD in docker-compose.yml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -25,9 +25,9 @@ services:
     image: postgis/postgis:16-3.4
     restart: unless-stopped
     environment:
-      POSTGRES_DB: ${POSTGRES_DB:-sargasses}
-      POSTGRES_USER: ${POSTGRES_USER:-app}
-      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+      POSTGRES_DB: ${POSTGRES_DB:-sargasses_db}
+      POSTGRES_USER: ${POSTGRES_USER:-rs971_user}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-changeme}
     volumes:
       - db_data:/var/lib/postgresql/data
     networks: