feat(skin): add audio skins for HTML and React presets (#772)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

build/plugins/copy-css-plugin.mjs

@@ -0,0 +1,31 @@
+import { globSync, mkdirSync, readFileSync, writeFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { resolveImports } from './resolve-css-imports.mjs';
+
+/**
+ * @param {{ skinsDir: string; outDir: string }} options
+ */
+export function copyCssPlugin(options) {
+  const { skinsDir, outDir } = options;
+
+  return {
+    name: 'copy-css',
+    buildStart() {
+      for (const file of globSync('src/**/*.css')) {
+        this.addWatchFile(file);
+      }
+      for (const file of globSync(join(skinsDir, '**/*.css'))) {
+        this.addWatchFile(file);
+      }
+    },
+    writeBundle() {
+      for (const file of globSync('src/**/*.css')) {
+        const content = readFileSync(file, 'utf-8');
+        const resolved = resolveImports(content, dirname(file), skinsDir);
+        const outFile = join(outDir, file.replace(/^src\//, ''));
+        mkdirSync(dirname(outFile), { recursive: true });
+        writeFileSync(outFile, resolved);
+      }
+    },
+  };
+}