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>

frontend-v2/src/modules/aia/styles/chat-workspace.css

@@ -1005,15 +1005,11 @@
 
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@@ -1034,4 +1030,4 @@
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