feat: add intelligent backend routing and model service

- Add modelService for centralized model management
  - Support dynamic model list from config file (data/supported_models.json)
  - Include 2025 latest models: GPT-4.1, o3, o4-mini, Gemini 2.5, etc.
  - File watcher for hot-reload configuration changes

- Improve model detection logic in api.js
  - Priority: modelService lookup → prefix matching fallback
  - Smart backend routing based on model provider

- Add intelligent routing endpoints
  - /v1/chat/completions: unified OpenAI-compatible endpoint
  - /v1/completions: legacy format support
  - Auto-route to Claude/OpenAI/Gemini based on requested model

- Add Xcode system prompt support in openaiToClaude
  - Detect and preserve Xcode-specific system messages

- Export handler functions for reuse
  - openaiClaudeRoutes: export handleChatCompletion
  - openaiRoutes: export handleResponses

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

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

src/app.js

@@ -55,6 +55,11 @@ class Application {
       logger.info('🔄 Initializing pricing service...')
       await pricingService.initialize()
 
+      // 📋 初始化模型服务
+      logger.info('🔄 Initializing model service...')
+      const modelService = require('./services/modelService')
+      await modelService.initialize()
+
       // 📊 初始化缓存监控
       await this.initializeCacheMonitoring()
 
@@ -630,6 +635,15 @@ class Application {
             logger.error('❌ Error cleaning up pricing service:', error)
           }
 
+          // 清理 model service 的文件监听器
+          try {
+            const modelService = require('./services/modelService')
+            modelService.cleanup()
+            logger.info('📋 Model service cleaned up')
+          } catch (error) {
+            logger.error('❌ Error cleaning up model service:', error)
+          }
+
           // 停止限流清理服务
           try {
             const rateLimitCleanupService = require('./services/rateLimitCleanupService')