fix(compose): use CMD form for pg_isready healthcheck, add start_period

CMD-SHELL drops pg_isready from PATH on some Alpine setups. Switch to
explicit CMD array form with -h 127.0.0.1. start_period gives postgres
time to initialize before failures count against retries.

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

docker-compose.yml

@@ -9,10 +9,11 @@ services:
     volumes:
       - postgres_data:/var/lib/postgresql/data
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U grow"]
+      test: ["CMD", "pg_isready", "-U", "grow", "-d", "grow", "-h", "127.0.0.1"]
       interval: 5s
       timeout: 5s
-      retries: 10
+      retries: 20
+      start_period: 15s
 
   app:
     build: .