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

.env.example

@@ -0,0 +1,33 @@
+# Local development environment file (copy to .env).
+# For production server values, use .env.prod.example instead.
+DJANGO_ENV=dev
+DJANGO_DEBUG=true
+DJANGO_SECRET_KEY=change-me-for-local-development
+DJANGO_ALLOWED_HOSTS=localhost,127.0.0.1,0.0.0.0
+# Optional; when unset, http:// origins are derived for local hosts.
+# DJANGO_CSRF_TRUSTED_ORIGINS=http://localhost:8003,http://127.0.0.1:8003
+
+# Database (docker-compose sets DATABASE_URL for the web service)
+DATABASE_URL=postgres://chat_backend:chat_backend@db:5432/chat_backend
+
+# Ollama — local loopback when Ollama runs on this machine; LAN IP for GPU host.
+OLLAMA_BASE_URL=http://127.0.0.1:11434
+# OLLAMA_MODEL=llama3.2
+# OLLAMA_EMBED_MODEL=llama3.2
+
+# Email (SMTP2GO) — optional for local
+EMAIL_HOST=mail.smtp2go.com
+EMAIL_HOST_USER=
+EMAIL_HOST_PASSWORD=
+EMAIL_PORT=2525
+EMAIL_USE_TLS=true
+
+# Captcha (optional local)
+CAPTCHA_SECRET_KEY=
+
+# Gunicorn / ASGI
+GUNICORN_WORKERS=2
+GUNICORN_BIND=0.0.0.0:8000
+
+# Host port for docker-compose.prod.yml
+WEB_PORT=8003