fix(samples): give playgrounds their own package names

Two playgrounds shipped duplicate @cpp.js/sample-* names (backend-nodejs and
backend-nodejs-multithread both claimed sample-backend-nodejs-wasm; the
multithread vite playground claimed playground-web-vite). The sample-* names
wrongly pulled them into CI's build:samples, where the geo-stack wasm dists
do not exist — previously masked by the silent exit-0 run path, now an honest
failure on build-linux.

Author: bugra9

cppjs-samples/cppjs-playground-backend-nodejs-multithread/package.json

@@ -1,5 +1,5 @@
 {
-    "name": "@cpp.js/sample-backend-nodejs-wasm",
+    "name": "@cpp.js/playground-backend-nodejs-multithread",
     "version": "2.0.0-beta.23",
     "private": true,
     "description": "Cpp.js - Node.js webassembly sample",

cppjs-samples/cppjs-playground-backend-nodejs/package.json

@@ -1,5 +1,5 @@
 {
-    "name": "@cpp.js/sample-backend-nodejs-wasm",
+    "name": "@cpp.js/playground-backend-nodejs",
     "version": "2.0.0-beta.23",
     "private": true,
     "description": "Cpp.js - Node.js webassembly sample",

cppjs-samples/cppjs-playground-web-vite-multithread/package.json

@@ -1,5 +1,5 @@
 {
-    "name": "@cpp.js/playground-web-vite",
+    "name": "@cpp.js/playground-web-vite-multithread",
     "version": "2.0.0-beta.23",
     "private": true,
     "description": "Cpp.js Vite Playground",