Dockerize chat_backend + Ollama LAN + DB file storage (#6) (#7)

## Summary

Implements [chat_backend#6](#6) Part A:

- **uv** packaging (`pyproject.toml` + `uv.lock`), Docker/compose (dev + prod), entrypoint/validate-env, Gitea unit-test + auto-deploy workflows (mirror `scha`)
- Env-driven Django settings (`DJANGO_*`, `DATABASE_URL`, CSRF/CORS)
- **`OLLAMA_BASE_URL`** wired through all Ollama/LangChain clients (prod → `http://10.0.0.128:11434`)
- **DatabaseStorage** — prompt/document file blobs in Postgres (`StoredFile`), not container FS; RAG materializes temp paths for loaders
- ASGI via `gunicorn` + `UvicornWorker` (HTTP + WebSockets)

Companion server-infra PR registers `app_catalog` / `host_apps` (port **8003**).

## Test plan

- [ ] `uv sync && cd llm_be && SKIP_RAG_INIT=1 uv run python manage.py test`
- [ ] `docker compose build && docker compose up` against bundled Postgres
- [ ] Confirm Ollama calls use `OLLAMA_BASE_URL` (not hardcoded localhost)
- [ ] Upload a document / prompt file → row in `chat_backend_storedfile`, no disk under `media/`
- [ ] After server-infra merge + secret/Postgres/NPM: deploy via `deploy.sh --app chat_backend --env prod`Reviewed-on: #7

docker-compose.yml

@@ -0,0 +1,40 @@
+services:
+  db:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_DB: chat_backend
+      POSTGRES_USER: chat_backend
+      POSTGRES_PASSWORD: chat_backend
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U chat_backend -d chat_backend"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+      start_period: 10s
+
+  web:
+    build: .
+    ports:
+      - "8003:8000"
+    # No required env_file — CI has no .env. Defaults below; for local secrets:
+    #   docker compose --env-file .env up
+    #
+    # Do NOT interpolate ${DATABASE_URL} here. On the Act runner / control node that
+    # var often points at shared prod/beta Postgres; compose would bake it into
+    # containerized tests. Use COMPOSE_DATABASE_URL only if you need to override.
+    environment:
+      DJANGO_ENV: ${DJANGO_ENV:-dev}
+      DJANGO_SECRET_KEY: ${DJANGO_SECRET_KEY:-dev-only-change-me}
+      DJANGO_DEBUG: ${DJANGO_DEBUG:-true}
+      DJANGO_ALLOWED_HOSTS: ${DJANGO_ALLOWED_HOSTS:-localhost,127.0.0.1,0.0.0.0,testserver}
+      DATABASE_URL: ${COMPOSE_DATABASE_URL:-postgres://chat_backend:chat_backend@db:5432/chat_backend}
+      OLLAMA_BASE_URL: ${OLLAMA_BASE_URL:-http://10.0.0.128:11434}
+      SKIP_RAG_INIT: ${SKIP_RAG_INIT:-1}
+    depends_on:
+      db:
+        condition: service_healthy
+
+volumes:
+  postgres_data: