Add Claude API support and fix CORS issues

- Add Claude API integration to LLM service
- Create Express backend server with CORS support
- Add API proxy example page
- Fix CORS errors by routing through backend
- Update LLM configuration to support Claude
- Add package.json with dependencies

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

routes/llm.routes.js

@@ -35,6 +35,15 @@ router.post('/test/openai', asyncHandler(async (req, res) => {
   res.json(result);
 }));
 
+/**
+ * POST /api/llm/test/claude
+ * 測試 Claude API 連線
+ */
+router.post('/test/claude', asyncHandler(async (req, res) => {
+  const result = await llmService.testClaudeConnection();
+  res.json(result);
+}));
+
 /**
  * POST /api/llm/test/all
  * 測試所有 LLM API 連線