The setup-python action has hardcoded paths that fail on self-hosted
macOS runners. Use system Python directly instead.
Also simplified clang-format step to use system version if available.
Adapt GitHub Actions workflows for self-hosted Gitea instance:
- CI workflow with PlatformIO build, cppcheck, and clang-format
- PR title format checker using conventional commits
- Release workflow for tagged builds
Keeps original .github/workflows/ for upstream compatibility.