feat: add vite-layers

vite-layers/example/apps/main/app.config.ts

@@ -0,0 +1,18 @@
+import vue from '@vitejs/plugin-vue'
+import { defineLayerConfig } from '../../../src/index.ts'
+
+export default defineLayerConfig({
+  name: 'main',
+  features: { billing: true, p2p: true },
+  // The framework plugin lives in the layer config, not in vite-layers' core.
+  vite: {
+    plugins: [vue()],
+    build: { rolldownOptions: { input: { main: '@/main.ts' } } },
+  },
+  // Per-layer tsconfig tweaks (merged across the stack, like Nuxt's typescript.tsConfig).
+  tsConfig: { compilerOptions: { jsx: 'preserve', jsxImportSource: 'vue' } },
+
+  $production: {
+    features: { p2p: false },
+  }
+})