feat: Rename to `scg`, single-file mode

Note

This is a breaking change from previous versions, primarily because the utility has been renamed toscg. User feedback was that the naming was both verbose (swiftcommitgen is a lot to type) and that the naming emphasis on 'swift' implied that it wouldn't work for diffs of other languages (and not just that the tool is written in swift).

Breaking Changes

• Renamed the executable from swiftcommitgen to scg; update any scripts, aliases, or CI workflows accordingly.
• Moved the persisted configuration to ~/Library/Application Support/scg/config.json (or the equivalent XDG path). Copy existing settings to the new location if you relied on the old swiftcommitgen directory.

What's New

• Added a per-file generation mode. Invoke it ad-hoc with scg generate --single-file or persist it via scg config --mode per-file.
• Expanded scg config with interactive and flag-driven controls for the default generation mode alongside existing auto-stage and verbosity settings (i.e., configure to use single file by default if you'd like).
• Surfaced detailed batch diagnostics when verbose logging is enabled to make prompt budgeting easier to understand.

Upgrade Tips

• Reinstall via the updated Scripts/install.sh or Homebrew formula to receive the renamed binary.
• If you maintained a previous configuration file, manually migrate it to the new scg directory before running scg config.