Add FxNode render graph playground

Add persistent render graph loadouts, grouped node authoring, code-appending apply behavior, explicit playground lighting, and resilient worker startup.

Amp-Thread-ID: https://ampcode.com/threads/T-01a033d4-0e44-708e-af0e-6166283416ff
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

server/packages_test.go

@@ -11,6 +11,8 @@ func TestLoadPackages(t *testing.T) {
 	for _, name := range []string{
 		"core.js",
 		"handles.js",
+		"fxnode-rg.js",
+		"fxnode-worker.js",
 		"worker.js",
 		"importer-worker.js",
 		"bvh-worker.js",
@@ -29,7 +31,7 @@ func TestLoadPackages(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if len(packages) != 6 {
+	if len(packages) != 8 {
 		t.Fatalf("package count = %d", len(packages))
 	}
 	if content := string(packages["pkg/yawn_core_bg.wasm"].content); content != filepath.Join("pkg", "yawn_core_bg.wasm") {