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.

IMPLEMENTATION_COMPLETE.md

@@ -671,7 +671,7 @@ docker-compose build
 docker-compose up -d
 
 # Indexar livros
-docker-compose run --rm web python backend/scripts/index_books.py
+docker compose run --rm web python scripts/index_books.py
 ```
 
 ### Produção - Single Server