feat(db): add postgres setup and multi-tenant config

docker-compose.yml

@@ -0,0 +1,57 @@
+version: '3.8'
+
+services:
+  # 1. PostgreSQL 16 Datenbank (Hybrid Multi-Tenant Storage)
+  postgres:
+    image: postgres:16-alpine
+    container_name: caspos-postgres
+    restart: unless-stopped
+    environment:
+      POSTGRES_DB: ${POSTGRES_DB:-caspos_reservations}
+      POSTGRES_USER: ${POSTGRES_USER:-caspos_admin}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-secretpassword}
+    ports:
+      - "${POSTGRES_PORT:-5432}:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+      - ./docker/postgres/init:/docker-entrypoint-initdb.d
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-caspos_admin} -d ${POSTGRES_DB:-caspos_reservations}"]
+      interval: 5s
+      timeout: 5s
+      retries: 5
+
+  # 2. Spring Boot 3 Java Backend (API)
+  backend:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    container_name: caspos-backend
+    restart: unless-stopped
+    depends_on:
+      postgres:
+        condition: service_healthy
+    environment:
+      SPRING_DATASOURCE_URL: jdbc:postgresql://postgres:5432/${POSTGRES_DB:-caspos_reservations}
+      SPRING_DATASOURCE_USERNAME: ${POSTGRES_USER:-caspos_admin}
+      SPRING_DATASOURCE_PASSWORD: ${POSTGRES_PASSWORD:-secretpassword}
+      SPRING_PROFILES_ACTIVE: docker
+    ports:
+      - "8080:8080"
+
+  # 3. TypeScript / React Frontend (Tischplan & UI)
+  frontend:
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile
+    container_name: caspos-frontend
+    restart: unless-stopped
+    depends_on:
+      - backend
+    environment:
+      NEXT_PUBLIC_API_URL: http://localhost:8080/api/v1
+    ports:
+      - "3000:3000"
+
+volumes:
+  postgres_data: