docs(iit): Add IIT Manager Agent V2.9 development plan with multi-agent architecture

Features:
- Add V2.9 enhancements: Cron Skill, User Profiling, Feedback Loop, Multi-Intent Handling
- Create modular development plan documents (database, engines, services, memory, tasks)
- Add V2.5/V2.6/V2.8/V2.9 design documents for architecture evolution
- Add system design white papers and implementation guides

Architecture:
- Dual-Brain Architecture (SOP + ReAct engines)
- Three-layer memory system (Flow Log, Hot Memory, History Book)
- ProfilerService for personalized responses
- SchedulerService with Cron Skill support

Also includes:
- Frontend nginx config updates
- Backend test scripts for WeChat signature
- Database backup files

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/test-wechat-signature.js

@@ -0,0 +1,22 @@
+const crypto = require('crypto');
+
+const token = 'IitPatientWechat2026JanToken';
+const timestamp = '1234567890';
+const nonce = 'test123';
+
+// 字典序排序
+const arr = [token, timestamp, nonce].sort();
+console.log('Sorted array:', arr);
+
+// 拼接字符串
+const str = arr.join('');
+console.log('Concatenated string:', str);
+
+// SHA1 加密
+const hash = crypto.createHash('sha1').update(str).digest('hex');
+console.log('Calculated signature:', hash);
+
+// 使用这个签名测试
+console.log('');
+console.log('Test URL:');
+console.log(`curl "https://iit.xunzhengyixue.com/wechat/patient/callback-plain?signature=${hash}&timestamp=${timestamp}&nonce=${nonce}&echostr=hello"`);