feat(iit-manager): Add WeChat Official Account integration for patient notifications

Features:
- PatientWechatCallbackController for URL verification and message handling
- PatientWechatService for template and customer messages
- Support for secure mode (message encryption/decryption)
- Simplified route /wechat/patient/callback for WeChat config
- Event handlers for subscribe/unsubscribe/text messages
- Template message for visit reminders

Technical details:
- Reuse @wecom/crypto for encryption (compatible with Official Account)
- Relaxed Fastify schema validation to prevent early request blocking
- Access token caching (7000s with 5min pre-refresh)
- Comprehensive logging for debugging

Testing: Local URL verification passed, ready for SAE deployment

Status: Code complete, waiting for WeChat platform configuration

backend/WECHAT_ENV_CONFIG.md

@@ -1,4 +1,4 @@
-# 企业微信环境变量配置说明
+# 微信环境变量配置说明（企业微信 + 服务号）
 
 ## 📋 必需的环境变量
 
@@ -6,7 +6,7 @@
 
 ```env
 # ==========================================
-# 企业微信配置
+# 企业微信配置（研究者端）
 # ==========================================
 
 # 企业微信基础配置（应用信息）
@@ -20,6 +20,21 @@ WECHAT_ENCODING_AES_KEY=V88eT3O9bMW897h4btr7v7qvQlmlMf31edTQCmuhOhO
 
 # 测试用户ID（可选，仅测试环境使用）
 WECHAT_TEST_USER_ID=FengZhiBo
+
+# ==========================================
+# 微信服务号配置（患者端）
+# ==========================================
+
+# 微信服务号基础配置
+WECHAT_MP_APP_ID=wx062568ff49e4570c
+WECHAT_MP_APP_SECRET=c0d19435d1a1e948939c16d767ec0faf
+
+# 微信服务号回调配置（消息加解密，安全模式）
+WECHAT_MP_TOKEN=<需要生成3-32位字符串>
+WECHAT_MP_ENCODING_AES_KEY=<需要生成43位字符串>
+
+# 微信小程序配置（可选，后续开发）
+WECHAT_MINI_APP_ID=<待申请>
 ```
 
 ## 📝 配置项说明