fix: add setup service for db push/seed; update README

The production runner image has no node_modules, so prisma CLI and tsx
are unavailable. Add a Compose 'setup' profile service that uses the
builder stage (which has all dev tools) to run db push and db seed.

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

docker-compose.yml

@@ -33,5 +33,23 @@ services:
       retries: 3
       start_period: 60s
 
+  # First-run setup: applies the schema and seeds the user.
+  # Uses the builder stage so all dev tools (prisma CLI, tsx, bcryptjs) are available.
+  # Run once with: docker compose --profile setup run --rm setup
+  setup:
+    build:
+      context: .
+      target: builder
+    command: sh -c "npx prisma db push && npx prisma db seed"
+    environment:
+      DATABASE_URL: postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:5432/${POSTGRES_DB}
+      SEED_EMAIL: ${SEED_EMAIL}
+      SEED_PASSWORD: ${SEED_PASSWORD}
+    depends_on:
+      db:
+        condition: service_healthy
+    profiles:
+      - setup
+
 volumes:
   postgres_data: