refactor(srp): add managed lifecycle cleanup seams

Invoke managed pipeline disposal and asset runtime cleanup from the native bridge lifecycle. Add Universal renderer and feature cleanup hooks plus regression probes to verify runtime cache teardown semantics.

managed/XCEngine.ScriptCore/Rendering/Core/ScriptableRenderPipeline.cs

@@ -4,10 +4,23 @@ namespace XCEngine.Rendering
 {
     public abstract class ScriptableRenderPipeline : Object
     {
+        private bool m_disposed;
+
         protected ScriptableRenderPipeline()
         {
         }
 
+        internal void DisposeInstance()
+        {
+            if (m_disposed)
+            {
+                return;
+            }
+
+            Dispose(true);
+            m_disposed = true;
+        }
+
         protected virtual bool SupportsStageRenderGraph(
             CameraFrameStage stage)
         {
@@ -19,6 +32,11 @@ namespace XCEngine.Rendering
         {
             return false;
         }
+
+        protected virtual void Dispose(
+            bool disposing)
+        {
+        }
     }
 }