docs: unify codebase assistant phase status in README

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

Author: anhmtk

README.md

@@ -456,7 +456,7 @@ StillMe can understand and explain its own codebase using RAG-based code retriev
 **Endpoint:** `POST /api/codebase/query` - Query codebase with questions  
 **Stats:** `GET /api/codebase/stats` - Collection statistics
 
-**Status:** ✅ Phase 1 (Code Q&A) | 🚧 Phase 2 (Test Generation) In Progress
+**Status:** ✅ Phase 3 Complete (Code Q&A + Test Generation + Code Review + Git History + Onboarding Mentor)
 
 📚 **Full Documentation**: [`docs/CODEBASE_ASSISTANT.md`](docs/CODEBASE_ASSISTANT.md)