fix(backend): Resolve duplicate /health route registration

- Move /health route into registerHealthRoutes function for backward compatibility
- Update index.ts to only call registerHealthRoutes once
- Now provides 3 endpoints: /health, /health/liveness, /health/readiness

Fixes: FastifyError Method 'GET' already declared for route '/health'

backend/src/common/health/healthCheck.ts

@@ -18,9 +18,10 @@ export interface HealthCheckResponse {
 /**
  * 注册健康检查路由
  * 
- * 提供两个端点：
- * 1. /health/liveness - SAE存活检查（简单响应）
- * 2. /health/readiness - SAE就绪检查（检查依赖服务）
+ * 提供三个端点：
+ * 1. /health - 向后兼容的简化健康检查
+ * 2. /health/liveness - SAE存活检查（简单响应）
+ * 3. /health/readiness - SAE就绪检查（检查依赖服务）
  * 
  * @example
  * ```typescript
@@ -31,6 +32,32 @@ export interface HealthCheckResponse {
  * ```
  */
 export async function registerHealthRoutes(app: FastifyInstance): Promise<void> {
+  /**
+   * 简化健康检查（向后兼容）
+   * 
+   * GET /health
+   */
+  app.get('/health', async (
+    _request: FastifyRequest,
+    reply: FastifyReply
+  ) => {
+    // 检查数据库连接
+    let dbStatus = 'unknown'
+    try {
+      await prisma.$queryRaw`SELECT 1`
+      dbStatus = 'connected'
+    } catch {
+      dbStatus = 'disconnected'
+    }
+
+    return reply.status(200).send({
+      status: 'ok',
+      database: dbStatus,
+      timestamp: new Date().toISOString(),
+      uptime: process.uptime()
+    })
+  })
+
   /**
    * 存活检查（Liveness Probe）
    * 
@@ -219,3 +246,4 @@ export async function registerHealthRoutes(app: FastifyInstance): Promise<void>
   console.log('  - GET /health (detailed)')
 }
 
+