perf(deploy): flatten-session caching, bulk DeploySiteAsync, paged management queries

src/ZB.MOM.WW.ScadaBridge.DeploymentManager/IFlatteningPipeline.cs

@@ -23,11 +23,29 @@ public interface IFlatteningPipeline
     /// which need only the flattened config + revision hash, not a compile. Structural and
     /// semantic validation still run in both cases.
     /// </param>
+    /// <param name="session">
+    /// Optional flatten session memoising template-chain, composition and
+    /// session-global repository reads. Pass one shared session when flattening
+    /// several instances in a batch (see <c>DeploymentService.DeploySiteAsync</c>)
+    /// so a template chain shared by N instances is walked once. When
+    /// <see langword="null"/> the pipeline creates a private single-use session,
+    /// which still de-duplicates the repeated composed-chain loads inside one
+    /// instance's flatten. Additive parameter — existing callers are unaffected.
+    /// </param>
     /// <returns>A task that resolves to the flattened configuration, revision hash, and validation result; or a failure result if flattening could not complete.</returns>
     Task<Result<FlatteningPipelineResult>> FlattenAndValidateAsync(
         int instanceId,
         CancellationToken cancellationToken = default,
-        bool validateScripts = true);
+        bool validateScripts = true,
+        FlattenSession? session = null);
+
+    /// <summary>
+    /// Creates a fresh <see cref="FlattenSession"/> bound to this pipeline's
+    /// watermark, for a caller that wants to share one across a batch of
+    /// <see cref="FlattenAndValidateAsync"/> calls.
+    /// </summary>
+    /// <returns>A new, empty session.</returns>
+    FlattenSession CreateSession();
 }
 
 /// <summary>