Add SiteStreamGrpcClient.SubscribeSiteAsync mirroring SubscribeAsync but for
the site-wide, alarm-only SubscribeSite RPC: builds a SiteStreamRequest, opens
the server stream, and delivers each event via a typed Action<AlarmStateChanged>
callback (this stream is alarm-only by contract, so Task 4's per-site cache
consumes an alarm delta with no downstream type test). Reuses the shared
enrichment mapping via a new internal ConvertToAlarmEvent helper that returns
null for any non-alarm event, defensively filtering anything that should never
appear on the stream. Factory unchanged - it already caches a client per
(site, endpoint). Adds focused unit tests for the alarm-only filter and the
test-only-client guard.
Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj
Joseph Doherty
6d5ecc92a5