Migrate the backend from pip to uv

Replace requirements.txt with a uv workspace and lockfile, install the five tavolo packages from packages/* in development and non-editable in the image, and build the Docker image with uv. Move dev tools to a PEP 735 dependency group and refresh the locked dependency versions.

server/packages/tavolo-scopa/README.md

@@ -36,8 +36,8 @@ application composition root.
 ## Development (from `server/`)
 
 ```sh
-.venv/bin/python -m unittest discover -s packages/tavolo-scopa/tests
-.venv/bin/python -m mypy -p tavolo.scopa
+uv run python -m unittest discover -s packages/tavolo-scopa/tests
+uv run mypy -p tavolo.scopa
 ```
 
 `test_engine.py` covers the pure rules; `test_plugin.py` covers the