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>

config/llm.config.js

@@ -33,8 +33,18 @@ const llmConfig = {
     timeout: 30000,
   },
 
+  // Claude Configuration
+  claude: {
+    apiKey: process.env.CLAUDE_API_KEY,
+    apiUrl: process.env.CLAUDE_API_URL || 'https://api.anthropic.com/v1',
+    model: process.env.CLAUDE_MODEL || 'claude-3-5-sonnet-20241022',
+    enabled: !!process.env.CLAUDE_API_KEY,
+    timeout: 30000,
+    version: '2023-06-01', // Anthropic API version
+  },
+
   // Default LLM Provider
-  defaultProvider: 'gemini',
+  defaultProvider: 'claude',
 
   // Common Settings
   maxTokens: 2000,
@@ -49,6 +59,7 @@ function getEnabledProviders() {
   if (llmConfig.gemini.enabled) enabled.push('gemini');
   if (llmConfig.deepseek.enabled) enabled.push('deepseek');
   if (llmConfig.openai.enabled) enabled.push('openai');
+  if (llmConfig.claude.enabled) enabled.push('claude');
   return enabled;
 }