perf(siteruntime): projected single-row deployed-config reads (P1-4)

HandleEnsureInstanceStarted, HandleDeploymentStateQuery, and HandleEnable each
called GetAllDeployedConfigsAsync — materializing every deployed config,
including every ConfigJson blob — just to FirstOrDefault one row. A
volume-restore reconcile healing hundreds of instances turned that into
hundreds of full-table reads.

Add SiteStorageService.GetDeployedConfigAsync(name) (single-row, full
projection incl. ConfigJson, for callers that (re)start an Instance Actor)
and GetDeployedConfigMetadataAsync(name) (single-row, ConfigJson-free
projection, for callers that only need DeploymentId/RevisionHash/IsEnabled).
Switch the three call sites; leave decisions/semantics identical.

HandleEnsureInstanceStarted gets its own _deployedConfigLoader seam,
deliberately separate from the existing _configLoader (still used by the
boot-time load, which legitimately needs every row) so a test overriding one
cannot accidentally gate the other. Generation fencing (StoreGenerationAtRead,
Medium wave T1) is untouched: the generation is still captured on the actor
thread before the read dispatches.

Tests: new SiteStorageServiceTests lock in that both projections return the
same values GetAllDeployedConfigsAsync().FirstOrDefault(...) did. The three
row-101 ensure-started race tests (ReconcileStartsInstanceTests) are ported
to the new seam and still pass, proving generation fencing survives the
projection. Proof of failure: since this is a pure I/O-cost fix with no
observable behavior change, the new/changed tests were confirmed to fail to
even compile against the unfixed code (stash/unstash) — GetDeployedConfigAsync,
GetDeployedConfigMetadataAsync, and the deployedConfigLoader ctor param don't
exist there.

tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/ReconcileStartsInstanceTests.cs

@@ -92,7 +92,8 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
     /// </summary>
     private IActorRef CreateDeploymentManager(
         IServiceProvider? serviceProvider = null,
-        Func<Task<List<DeployedInstance>>>? configLoader = null)
+        Func<Task<List<DeployedInstance>>>? configLoader = null,
+        Func<string, Task<DeployedInstance?>>? deployedConfigLoader = null)
     {
         var health = new DeploymentManagerStartupProbe();
         var dm = ActorOf(Props.Create(() => new DeploymentManagerActor(
@@ -109,7 +110,11 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
             configFetcher: null,
             // In position: an expression tree rejects a named argument that skips a parameter.
             startupLoadRetryInterval: null,
-            configLoader: configLoader)));
+            configLoader: configLoader,
+            externalSystemCache: null,
+            scriptScheduler: null,
+            connectionDefinitionLoader: null,
+            deployedConfigLoader: deployedConfigLoader)));
 
         AwaitCondition(() => health.ReportCount > 0, TimeSpan.FromSeconds(20),
             TimeSpan.FromMilliseconds(25));
@@ -409,7 +414,7 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
     {
         const string instanceName = "RacedDisablePump";
         var loader = new GatedConfigLoader(_storage);
-        var dm = CreateDeploymentManager(configLoader: loader.LoadAsync);
+        var dm = CreateDeploymentManager(deployedConfigLoader: loader.LoadAsync);
 
         await _storage.StoreDeployedConfigAsync(
             instanceName, MakeConfigJson(instanceName), "dep-rd", "rev-rd", true);
@@ -451,7 +456,7 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
     {
         const string instanceName = "RacedDeletePump";
         var loader = new GatedConfigLoader(_storage);
-        var dm = CreateDeploymentManager(configLoader: loader.LoadAsync);
+        var dm = CreateDeploymentManager(deployedConfigLoader: loader.LoadAsync);
 
         await _storage.StoreDeployedConfigAsync(
             instanceName, MakeConfigJson(instanceName), "dep-rx", "rev-rx", true);
@@ -487,7 +492,7 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
     {
         const string instanceName = "UnracedPump";
         var loader = new GatedConfigLoader(_storage);
-        var dm = CreateDeploymentManager(configLoader: loader.LoadAsync);
+        var dm = CreateDeploymentManager(deployedConfigLoader: loader.LoadAsync);
 
         await _storage.StoreDeployedConfigAsync(
             instanceName, MakeConfigJson(instanceName), "dep-ok", "rev-ok", true);
@@ -510,15 +515,15 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
             .ResolveOne(TimeSpan.FromSeconds(5));
 
     /// <summary>
-    /// A deployed-config loader that can be held open mid-read, so a test can commit a
-    /// lifecycle write while a heal's snapshot is provably in flight rather than hoping the
-    /// two race the right way round.
+    /// A single-instance deployed-config loader that can be held open mid-read, so a test can
+    /// commit a lifecycle write while a heal's snapshot is provably in flight rather than hoping
+    /// the two race the right way round.
     ///
     /// <para>
     /// Reads real storage every time and only parks AFTER the read, so the returned snapshot is
     /// exactly what production would have seen at that instant. Inert until <see cref="Arm"/>
-    /// is called, which keeps the Deployment Manager's boot load (which runs through this same
-    /// seam) unblocked.
+    /// is called, which keeps the Deployment Manager's boot load — a separate seam
+    /// (<c>_configLoader</c>, register P1-4) untouched by this gate — unblocked.
     /// </para>
     /// </summary>
     private sealed class GatedConfigLoader(SiteStorageService storage)
@@ -534,16 +539,16 @@ public class ReconcileStartsInstanceTests : TestKit, IDisposable
 
         public Task WaitUntilParkedAsync() => _parked.Task.WaitAsync(TimeSpan.FromSeconds(10));
 
-        public async Task<List<DeployedInstance>> LoadAsync()
+        public async Task<DeployedInstance?> LoadAsync(string instanceName)
         {
-            var configs = await storage.GetAllDeployedConfigsAsync();
+            var config = await storage.GetDeployedConfigAsync(instanceName);
             var gate = _release;
             if (gate != null)
             {
                 _parked.TrySetResult();
                 await gate.Task;
             }
-            return configs;
+            return config;
         }
     }