infra(docker-compose): add full-stack development environment

Implements Task 22: Docker Compose Full Stack with Hot Reload

Services added:
- dotnet-api: Builds from backend/Dockerfile.dev
  - Port 5000→8080, volume mount for hot reload
  - Development environment with database + Keycloak config
  - Depends on: postgres (healthy), keycloak (healthy)

- nextjs: Builds from frontend/Dockerfile.dev
  - Port 3000, volume mount with node_modules exclusion
  - API URLs, NextAuth, Keycloak config
  - Depends on: dotnet-api

Dependency chain: postgres → keycloak → dotnet-api → nextjs

Features:
- Hot reload enabled via volume mounts with :cached flag (macOS)
- Backend runs migrations + seed on startup (Development mode)
- dotnet watch monitors backend changes
- bun run dev monitors frontend changes
- All services on app-network bridge

Environment variables configured for local development.

Note: Docker build/runtime verification skipped (Docker daemon unavailable).

docker-compose.yml

@@ -58,6 +58,51 @@ services:
       start-dev
       --import-realm
 
+  dotnet-api:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile.dev
+    container_name: workclub_api
+    environment:
+      ASPNETCORE_ENVIRONMENT: Development
+      ConnectionStrings__DefaultConnection: "Host=postgres;Port=5432;Database=workclub;Username=workclub;Password=dev_password_change_in_production"
+      Keycloak__Authority: "http://keycloak:8080/realms/workclub"
+      Keycloak__Audience: "workclub-api"
+    ports:
+      - "5000:8080"
+    volumes:
+      - ./backend:/app:cached
+    depends_on:
+      postgres:
+        condition: service_healthy
+      keycloak:
+        condition: service_healthy
+    networks:
+      - app-network
+
+  nextjs:
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile.dev
+    container_name: workclub_frontend
+    environment:
+      NEXT_PUBLIC_API_URL: "http://localhost:5000"
+      API_INTERNAL_URL: "http://dotnet-api:8080"
+      NEXTAUTH_URL: "http://localhost:3000"
+      NEXTAUTH_SECRET: "dev-secret-change-in-production-use-openssl-rand-base64-32"
+      KEYCLOAK_ID: "workclub-api"
+      KEYCLOAK_SECRET: "dev-secret-workclub-api-change-in-production"
+      KEYCLOAK_ISSUER: "http://localhost:8080/realms/workclub"
+    ports:
+      - "3000:3000"
+    volumes:
+      - ./frontend:/app:cached
+      - /app/node_modules
+    depends_on:
+      - dotnet-api
+    networks:
+      - app-network
+
 volumes:
   postgres-data:
     driver: local