fix: Implement mesh transform updates via helper function for CI/CD compatibility

The previous fix directly edited the generated app_gen.go file, which would
be lost when CI/CD regenerates the code. This commit implements a proper
solution that survives code regeneration.

Changes:
- Created helpers.go with updateMeshTransform() function
- Updated app.gx to call helper from renderUpdate callback
- Regenerated app_gen.go now calls the helper function
- Helper contains the mesh transform update logic

The helper function:
- Casts rendererInterface to *SceneRenderer
- Creates a Transform with current rotation values
- Calls UpdateMeshTransform to apply the rotation on every frame

This approach works because:
1. helpers.go is not generated, so it won't be overwritten
2. The simple function call in app.gx is supported by the Guix DSL parser
3. Code regeneration preserves the helper function call
4. Both auto-rotation and manual controls now work correctly

Author: claude

examples/webgpu-cube/app.gx

@@ -53,6 +53,7 @@ func App() (Component) {
 			rotationY = rotationY + (delta * speed)
 			rotationX = rotationX + (delta * speed * 0.5)
 		}
+		updateMeshTransform(rendererInterface, rotationX, rotationY)
 	}
 
 	Div(

examples/webgpu-cube/app_gen.go

@@ -0,0 +1,18 @@
+//go:build js && wasm
+
+package main
+
+import (
+	"github.com/gaarutyunov/guix/pkg/runtime"
+)
+
+// updateMeshTransform updates the mesh transform with the given rotation values
+func updateMeshTransform(rendererInterface interface{}, rotationX, rotationY float64) {
+	if renderer, ok := rendererInterface.(*runtime.SceneRenderer); ok && len(renderer.Meshes) > 0 {
+		transform := runtime.NewTransform()
+		transform.Position = runtime.Vec3{X: 0, Y: 0, Z: 0}
+		transform.Rotation = runtime.Vec3{X: float32(rotationX), Y: float32(rotationY), Z: 0}
+		transform.Scale = runtime.Vec3{X: 1, Y: 1, Z: 1}
+		renderer.UpdateMeshTransform(0, transform)
+	}
+}