wp-stage-syncLive

Add a settings screen to the TUI, accessible via the s shortcut from the first screen. Update footer unconditionally to show the shortcut — no config required to access it. Reads from and writes to ~/.config/wp-stage-sync/settings.json. If the file does not exist, create it with defaults on first write.

Initial settings:

• backup_retention (int, default: 5) — maximum number of backups to keep per domain. Editable as a numeric input with up/down arrow increment.

• auto_cache_flush (bool, default: true) — whether to run wp cache flush automatically after sync and push operations. Editable as a toggle.

Persist changes immediately on exit from the settings screen. All existing code that reads backup_retention or triggers cache flush must respect these values at runtime.