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

vue-sync-engine/lib/vitest.config.ts

@@ -0,0 +1,49 @@
+/// <reference types="vitest/config" />
+import { defineConfig } from 'vite'
+import { playwright } from '@vitest/browser-playwright'
+import { syncEnginePlugin } from './src/plugin'
+
+export default defineConfig({
+  // The lib's own DevTools setup does `import('virtual:sync-engine-registry')`;
+  // register the plugin (with no matching defs in lib/) so Vite can resolve
+  // the virtual module to an empty registry instead of throwing at transform.
+  plugins: [syncEnginePlugin({ definitions: ['/lib/**/*.defs.ts'] })],
+  define: {
+    __VUE_OPTIONS_API__: 'true',
+    __VUE_PROD_DEVTOOLS__: 'false',
+    __VUE_PROD_HYDRATION_MISMATCH_DETAILS__: 'false',
+    // Enable dev-only assertions and DevTools branches in the lib source.
+    __SYNC_ENGINE_DEV__: 'true',
+  },
+  test: {
+    include: ['src/**/*.{test,spec}.ts'],
+    globals: false,
+    browser: {
+      enabled: true,
+      provider: playwright(),
+      headless: true,
+      screenshotFailures: false,
+      instances: [{ browser: 'chromium' }],
+    },
+    coverage: {
+      provider: 'v8',
+      include: ['src/**/*.ts'],
+      exclude: [
+        'src/**/__tests__/**',
+        'src/index.ts',
+        'src/__dev.ts',
+        'src/core/types.ts',
+        'src/core/keyedStore.ts',
+        'src/transport/protocol.ts',
+        'src/devtools.ts',
+      ],
+      reporter: ['text', 'html'],
+      thresholds: {
+        statements: 90,
+        branches: 75,
+        functions: 90,
+        lines: 95,
+      },
+    },
+  },
+})