fix: use append (>>) instead of overwrite (>) for cron logs and add missing dependencies

- Fixed api/schema.py to generate cron jobs using '>> wecker.log' so logs aren't truncated.
- Added test_bugfix_default_command_uses_append_for_logs in tests/test_api.py to prevent regression.
- Added RPi.GPIO and pygame to pyproject.toml via 'uv add' to fix ModuleNotFoundError in cron jobs.
- Updated README.md to reflect that system python packages are no longer needed.

README.md

@@ -21,10 +21,6 @@ This project uses Python 3 and `uv` for dependency management. To set up the env
    uv sync
    ```
 
-Note: The system also requires `python3-pygame` and `python3-rpi.gpio` which should be installed via system packages:
-```bash
-sudo apt-get install python3-pygame python3-rpi.gpio
-```
 
 
 ## Wiring