chore: update justfile commands and parameterize healthcheck info

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

compose.yml

@@ -11,7 +11,7 @@ services:
     volumes:
       - loft_db_data:/var/lib/postgresql/data
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U postgres -d loft"]
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
       interval: 5s
       timeout: 5s
       retries: 5
@@ -21,7 +21,7 @@ services:
     restart: unless-stopped
     build: .
     ports:
-      - "3000:3000"    
+      - "3000:3000"
     depends_on:
       db:
         condition: service_healthy