refactor(core): Unify package exports and improve dev experience

- Update license header to include Qwen copyright
- Add error handler for spawn in dev.js
- Refactor core/src/index.ts to export all public APIs
- Simplify core/index.ts to be a clean re-export
- Fix vitest alias to point to package entry

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

scripts/dev.js

@@ -1,6 +1,6 @@
 /**
  * @license
- * Copyright 2025 Google LLC
+ * Copyright 2025 Qwen
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -84,6 +84,16 @@ const child = spawn('node', nodeArgs, {
   cwd: process.cwd(),
 });
 
+child.on('error', (err) => {
+  console.error('Failed to start dev server:', err.message);
+  try {
+    rmSync(tmpDir, { recursive: true, force: true });
+  } catch {
+    // Ignore cleanup errors
+  }
+  process.exit(1);
+});
+
 child.on('close', (code) => {
   // Cleanup temp directory
   try {