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.

pyproject.toml

@@ -6,8 +6,10 @@ readme = "README.md"
 requires-python = ">=3.13"
 dependencies = [
     "fastapi>=0.136.1",
+    "pygame>=2.6.1",
     "python-crontab>=3.3.0",
     "python-dotenv>=1.2.2",
+    "rpi-gpio>=0.7.1",
     "strawberry-graphql>=0.315.3",
     "uvicorn>=0.46.0",
 ]