Add shared config.toml storage while keeping settings types, defaults and UI policy in each app.
Includes isolated in-memory operation, configurable portable paths, atomic saves with private backups, damaged-file preservation, schema migrations, and documented best-effort handling of external edits.
Validation: native macOS formatting, strict workspace clippy, 172 workspace tests and the craft-settings WASM check. Independent backup-permission and failed external-migration repros fail before the fixes and pass afterward.
Hosted CI: all seven UI and printing jobs pass across macOS, Linux, Windows and UI WASM.
Refs #12
