feat: compose stack in devcontainer (db, langflow, lfx)

- docker-compose.yml with app/db/langflow/lfx services and healthchecks
- Dockerfile.lfx (stateless flow runtime on :6004)
- init-db.sql (langflow + test databases)
- devcontainer.json switched to compose mode with runServices
- setup.sh waits for compose services and requires .env

.devcontainer/docker-compose.yml

@@ -0,0 +1,91 @@
+# Compose stack for the kirche-einfach devcontainer.
+# VS Code attaches to the `app` service (see devcontainer.json); all values
+# come from the repo-root `.env` via `env_file` (no ${} interpolation needed).
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+      args:
+        FORGEJO_USERNAME: jonas
+    command: sleep infinity
+    volumes:
+      - ..:/workspaces/kirche-einfach:cached
+      - kirche-einfach-venv:/workspaces/kirche-einfach/backend/.venv
+      - kirche-einfach-node-modules:/workspaces/kirche-einfach/frontend/node_modules
+    env_file:
+      - ../.env
+    ports:
+      - "8000:8000" # FastAPI
+      - "3000:3000" # Vite
+
+  db:
+    image: postgres:16-trixie
+    env_file:
+      - ../.env
+    volumes:
+      - postgres-data:/var/lib/postgresql/data
+      - ./init-db.sql:/docker-entrypoint-initdb.d/init-db.sql:ro
+    ports:
+      - "5432:5432"
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+
+  langflow:
+    image: langflowai/langflow:1.12.0
+    depends_on:
+      db:
+        condition: service_healthy
+    env_file:
+      - ../.env
+    environment:
+      # Static values only; secrets/URLs come from ../.env via env_file
+      # (compose interpolates ${} from .devcontainer/.env, not the repo-root .env).
+      LANGFLOW_CONFIG_DIR: /app/langflow
+      LANGFLOW_HOST: 0.0.0.0
+      PORT: "7860"
+      LANGFLOW_AUTO_LOGIN: "false"
+      LANGFLOW_API_KEY_SOURCE: env
+    volumes:
+      - langflow-data:/app/langflow
+    ports:
+      - "7860:7860"
+    healthcheck:
+      test:
+        [
+          "CMD-SHELL",
+          "python -c \"import urllib.request; urllib.request.urlopen('http://localhost:7860/health', timeout=5)\"",
+        ]
+      interval: 10s
+      timeout: 5s
+      retries: 20
+      start_period: 60s
+
+  lfx:
+    build:
+      context: .
+      dockerfile: Dockerfile.lfx
+    volumes:
+      - lfx-data:/flows
+    ports:
+      - "6004:6004"
+    healthcheck:
+      test:
+        [
+          "CMD-SHELL",
+          "python -c \"import urllib.request; urllib.request.urlopen('http://localhost:6004/health', timeout=5)\"",
+        ]
+      interval: 10s
+      timeout: 5s
+      retries: 12
+      start_period: 30s
+
+volumes:
+  kirche-einfach-venv:
+  kirche-einfach-node-modules:
+  postgres-data:
+  langflow-data:
+  lfx-data: