Phase 7 Stream D — Historian alarm sink (SQLite store-and-forward + Galaxy.Host IPC contracts)

Phase 7 plan decisions #16, #17, #19, #21 implementation. Durable local SQLite queue
absorbs every qualifying alarm event; drain worker forwards batches to Galaxy.Host
(reusing the already-loaded 32-bit aahClientManaged DLLs) on an exponential-backoff
cadence; operator acks never block on the historian being reachable.

## New project Core.AlarmHistorian (net10)

- AlarmHistorianEvent — source-agnostic event shape (scripted alarms + Galaxy-native +
  AB CIP ALMD + any future IAlarmSource)
- IAlarmHistorianSink / NullAlarmHistorianSink — interface + disabled default
- IAlarmHistorianWriter — per-event outcome (Ack / RetryPlease / PermanentFail); Stream G
  wires the Galaxy.Host IPC client implementation
- SqliteStoreAndForwardSink — full implementation:
  - Queue table with AttemptCount / LastError / DeadLettered columns
  - DrainOnceAsync serialised via SemaphoreSlim
  - BackoffLadder 1s → 2s → 5s → 15s → 60s (cap)
  - DefaultCapacity 1,000,000 rows — overflow evicts oldest non-dead-lettered
  - DefaultDeadLetterRetention 30 days — sweeper purges on every drain tick
  - RetryDeadLettered operator action reattaches dead-letters to the regular queue
  - Writer-side exceptions treated as whole-batch RetryPlease (no data loss)

## New IPC contracts in Driver.Galaxy.Shared

- HistorianAlarmEventRequest — batched up to 100 events/request per plan Stream D.5
- HistorianAlarmEventResponse — per-event outcome (1:1 with request order)
- HistorianAlarmEventOutcomeDto enum (byte on the wire — Ack/RetryPlease/PermanentFail)
- HistorianAlarmEventDto — mirrors Core.AlarmHistorian.AlarmHistorianEvent
- HistorianConnectivityStatusNotification — Host pushes proactively when the SDK
  session drops so /alarms/historian flips red without waiting for the next drain
- MessageKind additions: 0x80 HistorianAlarmEventRequest / 0x81 HistorianAlarmEventResponse
  / 0x82 HistorianConnectivityStatus

## Tests — 14/14

SqliteStoreAndForwardSinkTests covers: enqueue→drain→Ack round-trip, empty-queue no-op,
RetryPlease bumps backoff + keeps row, Ack after Retry resets backoff, PermanentFail
dead-letters one row without blocking neighbors, writer exception treated as whole-batch
retry with error surfaced in status, capacity eviction drops oldest non-dead-lettered,
dead-letters purged past retention window, RetryDeadLettered requeues, ladder caps at
60s after 10 retries, Null sink reports Disabled status, null sink swallows enqueue,
ctor argument validation, disposed sink rejects enqueue.

## Totals
Full Phase 7 tests: 160 green (63 Scripting + 36 VirtualTags + 47 ScriptedAlarms +
14 AlarmHistorian). Stream G wires this into the real Galaxy.Host IPC pipe.

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared/Contracts/Framing.cs

@@ -60,6 +60,14 @@ public enum MessageKind : byte
     HostConnectivityStatus     = 0x70,
     RuntimeStatusChange        = 0x71,
 
+    // Phase 7 Stream D — historian alarm sink. Main server → Galaxy.Host batched
+    // writes into the Aveva Historian alarm schema via the already-loaded
+    // aahClientManaged DLLs. HistorianConnectivityStatus fires proactively from the
+    // Host when the SDK session transitions so diagnostics flip promptly.
+    HistorianAlarmEventRequest        = 0x80,
+    HistorianAlarmEventResponse       = 0x81,
+    HistorianConnectivityStatus       = 0x82,
+
     RecycleHostRequest         = 0xF0,
     RecycleStatusResponse      = 0xF1,