fix(deploy): auto-migrate on boot + seed admin credentials from env

- docker-compose.admin.yml: RUN_MIGRATIONS was hardcoded false → now
  uses ${RUN_MIGRATIONS:-true} so migrations run automatically on deploy
- Both compose files: expose Seed__SystemAdminPhone/Username/Password
  env vars so the seeder sets admin credentials without manual SQL
- .env.example: document SEED_ADMIN_* variables

On next deploy: migrations run, Username='admin' is patched on the
existing admin, and password is hashed from SEED_ADMIN_PASSWORD.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker-compose.admin.yml

@@ -28,7 +28,7 @@ services:
     environment:
       ASPNETCORE_ENVIRONMENT: "${ASPNETCORE_ENVIRONMENT:-Development}"
       ASPNETCORE_URLS: http://+:8080
-      RUN_MIGRATIONS: "false"
+      RUN_MIGRATIONS: "${RUN_MIGRATIONS:-true}"
       ConnectionStrings__DefaultConnection: "${DB_CONNECTION_STRING:-Host=postgres;Port=5432;Database=meezi;Username=meezi;Password=meezi_local_pass}"
       ConnectionStrings__Redis: redis:6379
       Jwt__Key: "${JWT_KEY:-dev-jwt-key-CHANGE-THIS-IN-PRODUCTION-min32chars}"
@@ -36,6 +36,9 @@ services:
       Cors__Origins__1: "${CORS_ORIGIN_0:-http://localhost:3101}"
       Kavenegar__ApiKey: "${KAVENEGAR_API_KEY:-}"
       Kavenegar__SenderNumber: "${KAVENEGAR_SENDER:-90005671}"
+      Seed__SystemAdminPhone: "${SEED_ADMIN_PHONE:-}"
+      Seed__SystemAdminUsername: "${SEED_ADMIN_USERNAME:-admin}"
+      Seed__SystemAdminPassword: "${SEED_ADMIN_PASSWORD:-}"
     ports:
       - "${ADMIN_API_PORT:-5081}:8080"
     healthcheck: