fix: make docker compose build and start the API

The image context was backend/, so COPY frontend/ failed. Build from the
repo root, place Python modules on the import path, and pin packages that
exist on PyPI. The web process no longer loads the LLM at startup.

README.md

@@ -185,7 +185,7 @@ docker-compose ps
 ### 5. Indexar os Livros
 
 ```bash
-docker-compose run --rm web python backend/scripts/index_books.py
+docker compose run --rm web python scripts/index_books.py
 ```
 
 Isso irá: