Phase 7 follow-up #247 — Galaxy.Host historian writer + SQLite sink activation

Closes the historian leg of Phase 7. Scripted alarm transitions now batch-flow
through the existing Galaxy.Host pipe + queue durably in a local SQLite store-
and-forward when Galaxy is the registered driver, instead of being dropped into
NullAlarmHistorianSink.

## GalaxyHistorianWriter (Driver.Galaxy.Proxy.Ipc)

IAlarmHistorianWriter implementation. Translates AlarmHistorianEvent →
HistorianAlarmEventDto (Stream D contract), batches via the existing
GalaxyIpcClient.CallAsync round-trip on MessageKind.HistorianAlarmEventRequest /
Response, maps per-event HistorianAlarmEventOutcomeDto bytes back to
HistorianWriteOutcome (Ack/RetryPlease/PermanentFail) so the SQLite drain
worker knows what to ack vs dead-letter vs retry. Empty-batch fast path.
Pipe-level transport faults (broken pipe, host crash) bubble up as
GalaxyIpcException which the SQLite sink's drain worker translates to
whole-batch RetryPlease per its catch contract.

## GalaxyProxyDriver implements IAlarmHistorianWriter

Marker interface lets Phase7Composer discover it via type check at compose
time. WriteBatchAsync delegates to a thin GalaxyHistorianWriter wrapping the
driver's existing _client. Throws InvalidOperationException if InitializeAsync
hasn't connected yet — the SQLite drain worker treats that as a transient
batch failure and retries.

## Phase7Composer.ResolveHistorianSink

Replaces the injected sink dep when any registered driver implements
IAlarmHistorianWriter. Constructs SqliteStoreAndForwardSink at
%ProgramData%/OtOpcUa/alarm-historian-queue.db (falls back to %TEMP% when
ProgramData unavailable, e.g. dev), starts the 2s drain timer, owns the sink
disposable for clean teardown. When no driver provides the writer, keeps the
NullAlarmHistorianSink wired by Program.cs (#246).

DisposeAsync now also disposes the owned SQLite sink in the right order:
bridge → engines → owned sink → injected fallback.

## Tests — 7 new GalaxyHistorianWriterMappingTests

ToDto round-trips every field; preserves null Comment; per-byte outcome enum
mapping (Ack / RetryPlease / PermanentFail) via [Theory]; unknown byte throws;
ctor null-guard. The IPC round-trip itself is covered by the live Host suite
(task #240) which constructs a real pipe.

Server.Phase7 tests: 34/34 still pass; Galaxy.Proxy tests: 25/25 (+7 = 32 total).

## Phase 7 production wiring chain — COMPLETE
- ✅ #243 composition kernel
- ✅ #245 scripted-alarm IReadable adapter
- ✅ #244 driver bridge
- ✅ #246 Program.cs wire-in
- ✅ #247 this — Galaxy.Host historian writer + SQLite sink activation

What unblocks now: task #240 live OPC UA E2E smoke. With a Galaxy driver
registered, scripted alarm transitions flow end-to-end through the engine →
SQLite queue → drain worker → Galaxy.Host IPC → Aveva Historian alarm schema.
Without Galaxy, NullSink keeps the engines functional and the queue dormant.

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy/GalaxyProxyDriver.cs

@@ -1,4 +1,5 @@
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy.Ipc;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;
 using IpcHostConnectivityStatus = ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts.HostConnectivityStatus;
@@ -22,6 +23,7 @@ public sealed class GalaxyProxyDriver(GalaxyProxyOptions options)
       IHistoryProvider,
       IRediscoverable,
       IHostConnectivityProbe,
+      IAlarmHistorianWriter,
       IDisposable
 {
     private GalaxyIpcClient? _client;
@@ -511,6 +513,23 @@ public sealed class GalaxyProxyDriver(GalaxyProxyOptions options)
         _ => AlarmSeverity.Critical,
     };
 
+    /// <summary>
+    ///     Phase 7 follow-up #247 — IAlarmHistorianWriter implementation. Forwards alarm
+    ///     batches to Galaxy.Host over the existing IPC channel, reusing the connection
+    ///     the driver already established for data-plane traffic. Throws
+    ///     <see cref="InvalidOperationException"/> when called before
+    ///     <see cref="InitializeAsync"/> has connected the client; the SQLite drain worker
+    ///     translates that to whole-batch RetryPlease per its catch contract.
+    /// </summary>
+    public Task<IReadOnlyList<HistorianWriteOutcome>> WriteBatchAsync(
+        IReadOnlyList<AlarmHistorianEvent> batch, CancellationToken cancellationToken)
+    {
+        if (_client is null)
+            throw new InvalidOperationException(
+                "GalaxyProxyDriver IPC client not connected — historian writes rejected until InitializeAsync completes");
+        return new GalaxyHistorianWriter(_client).WriteBatchAsync(batch, cancellationToken);
+    }
+
     public void Dispose() => _client?.DisposeAsync().AsTask().GetAwaiter().GetResult();
 }