chore: restructure vue-sync-engine workspace and remove unused files

vue-sync-engine/playground/vite.config.ts

@@ -0,0 +1,22 @@
+/// <reference types="node" />
+import { defineConfig } from 'vite'
+import vue from '@vitejs/plugin-vue'
+import VueDevTools from 'vite-plugin-vue-devtools'
+import { syncEnginePlugin } from 'vue-sync-engine/plugin'
+
+const enginePlugin = syncEnginePlugin({ definitions: ['/src/**/*.defs.ts'] })
+
+export default defineConfig({
+  plugins: [VueDevTools(), vue(), enginePlugin],
+  worker: {
+    plugins: () => [syncEnginePlugin({ definitions: ['/src/**/*.defs.ts'] })],
+  },
+  define: {
+    __VUE_OPTIONS_API__: 'false',
+    __VUE_PROD_DEVTOOLS__: 'false',
+    __VUE_PROD_HYDRATION_MISMATCH_DETAILS__: 'false',
+    // Strip dev-only assertions and DevTools setup in `vite build`; keep them
+    // in `vite dev` so the Sync Engine panel works while developing.
+    __SYNC_ENGINE_DEV__: JSON.stringify(process.env.NODE_ENV !== 'production'),
+  },
+})