Make AppRefresher generic (Option + Source payload)

[anthony1810]

Changes

• Make AppRefresher generic over two app-defined types: Option (OptionSet, what to refresh) and Source (Sendable payload, typically an enum carrying the fresh object)
• refresh(_ option:source:) — broadcast an option plus an optional payload; observers filter by option and receive the Source? payload
• AppRefreshAction<Option, Source> carries option, source, and a unique id per emission (same option twice still triggers)
• .appRefresherHost(option:source:) / .appRefresherHost(_:) and .onAppRefresh(_:behavior:perform:) with .onNextAppear (default) / .immediate
• Update README App Refresh Bus section + API reference
• 6 unit tests, all passing

Notes

• Payload travels via the Source enum's associated values — lets a consumer update without a local DB (e.g. a brand-new Session).
• Breaking change vs the 1.2.0 AppRefresher API.

[ThangKM]

LGTM