Dockerize chat_backend for server-infra deploy (closes #6).

Add uv packaging, env-driven Django settings, OLLAMA_BASE_URL (LAN GPU
host), DatabaseStorage for prompt/document blobs, compose/CI/deploy
workflows mirroring scha, and ASGI gunicorn+UvicornWorker for WebSockets.

docker-compose.prod.yml

@@ -0,0 +1,16 @@
+# Production compose for server-infra deploy. No bundled Postgres — use shared
+# external DB via DATABASE_URL in .env (see .env.prod.example).
+services:
+  web:
+    build: .
+    restart: unless-stopped
+    ports:
+      - "${WEB_PORT:-8003}:8000"
+    env_file:
+      - .env
+    volumes:
+      # Chroma vector index only (uploaded file blobs live in Postgres).
+      - chroma_data:/app/llm_be/chroma_db
+
+volumes:
+  chroma_data: