infra(docker): add Docker Compose with PostgreSQL and Keycloak

- Add docker-compose.yml (v3.9) with postgres:16-alpine and keycloak:26.1 services
- Configure PostgreSQL with separate workclub and keycloak databases
- Setup Keycloak with database backend, admin user, and realm import capability
- Create PostgreSQL init script to provision development databases and users
- Add placeholder realm-export.json for Keycloak realm configuration
- Configure healthchecks and app-network bridge for service discovery
- Document configuration and patterns in learnings.md

docker-compose.yml

@@ -0,0 +1,67 @@
+version: '3.9'
+
+services:
+  postgres:
+    image: postgres:16-alpine
+    container_name: workclub_postgres
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: postgres
+      POSTGRES_INITDB_ARGS: "-c default_transaction_isolation=read_committed -c max_connections=200"
+    ports:
+      - "5432:5432"
+    volumes:
+      - postgres-data:/var/lib/postgresql/data
+      - ./infra/postgres:/docker-entrypoint-initdb.d
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+      start_period: 10s
+    networks:
+      - app-network
+    command: >
+      postgres
+      -c default_transaction_isolation=read_committed
+      -c max_connections=200
+
+  keycloak:
+    image: quay.io/keycloak/keycloak:26.1
+    container_name: workclub_keycloak
+    environment:
+      KEYCLOAK_ADMIN: admin
+      KEYCLOAK_ADMIN_PASSWORD: admin
+      KC_DB: postgres
+      KC_DB_URL: jdbc:postgresql://postgres:5432/keycloak
+      KC_DB_USERNAME: keycloak
+      KC_DB_PASSWORD: keycloakpass
+      KC_HEALTH_ENABLED: "true"
+      KC_LOG_LEVEL: INFO
+    ports:
+      - "8080:8080"
+    volumes:
+      - ./infra/keycloak:/opt/keycloak/data/import
+    depends_on:
+      postgres:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD-SHELL", "curl -sf http://localhost:8080/health/ready || exit 1"]
+      interval: 10s
+      timeout: 5s
+      retries: 30
+      start_period: 30s
+    networks:
+      - app-network
+    command: >
+      start-dev
+      --import-realm
+
+volumes:
+  postgres-data:
+    driver: local
+
+networks:
+  app-network:
+    driver: bridge