docs: Complete Phase 4 migration documentation

Update documentation to reflect Phase 4 completion:
- Mark Phase 4 as complete in MIGRATION_STATUS.md
- Update executive summary with Phase 4 achievements
- Update CLAUDE.md migration status to reflect all phases complete
- Document removal of 29 legacy files
- Establish single source of truth: /capabilities/testdrive-jsui/js/

Phase 4 Cleanup Summary:
- ✅ Removed /markitect/static/js/ directory (all JS files)
- ✅ Removed /markitect/static/editor.js (unused)
- ✅ Preserved /markitect/static/css/ (still in use)
- ✅ Clean codebase with no duplicate JavaScript files

Migration Status: FULLY COMPLETE - All 4 phases done

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CLAUDE.md

@@ -11,24 +11,26 @@ TestDrive-JSUI is a standalone JavaScript UI rendering engine and testing framew
 
 ## Migration Status
 
-**✅ MIGRATION COMPLETE - Phase 3**
+**✅ MIGRATION FULLY COMPLETE - ALL PHASES**
 
-This capability migration is now **complete**. The main MarkiTect application exclusively uses the capability location for all JavaScript UI files.
+This capability migration is now **fully complete** including cleanup. The main MarkiTect application exclusively uses the capability location, and legacy files have been removed.
 
-**Current Status**: ✅ Phase 3 Complete (December 16, 2025)
+**Current Status**: ✅ Phase 4 Complete (December 16, 2025)
 - All 24 original JavaScript files copied to capability ✅
 - 84 automated tests passing (68 JS + 15 Python + 1 fixes) ✅
 - Templates updated to use capability location ✅
 - Main app **fully using capability** (no hybrid approach) ✅
 - Verified in both view and edit modes ✅
+- **Legacy files removed** - cleanup complete ✅
 
 **Key Facts**:
 - **Main app status**: Fully migrated to capability location
-- **Original files**: Preserved in `/markitect/static/js/` (not deleted, for rollback safety)
+- **Original files**: **REMOVED** from `/markitect/static/js/` (Phase 4 cleanup)
+- **Single source of truth**: All JavaScript in `/capabilities/testdrive-jsui/js/`
 - **Testing**: All rendering modes work correctly
-- **Next phase**: Phase 4 (cleanup) - can remove original files after extended verification
+- **Migration**: Fully complete - no further phases needed
 
-**Documentation**: See `MIGRATION_STATUS.md` for complete migration details, verification results, and Phase 4 recommendations.
+**Documentation**: See `MIGRATION_STATUS.md` for complete migration details, all phases, and final verification results.
 
 ## Build and Test Commands
 
@@ -188,9 +190,9 @@ Located in `pyproject.toml`:
 
 ### Migration Strategy (Copy-First)
 
-**Status**: ✅ Phase 3 Complete - See `MIGRATION_STATUS.md` for full details
+**Status**: ✅ ALL PHASES COMPLETE - See `MIGRATION_STATUS.md` for full details
 
-The capability follows a **copy-first, verify-later** migration principle:
+The capability followed a **copy-first, verify-later** migration principle:
 
 **Phase 1: Copy** ✅ COMPLETE (December 16, 2025)
 1. ✅ Copy all original files to `js/` directory
@@ -207,13 +209,13 @@ The capability follows a **copy-first, verify-later** migration principle:
 3. ✅ Maintain rollback capability (originals preserved)
 4. ✅ Monitor for issues (none found)
 
-**Phase 4: Cleanup** ⏸️ READY
-1. ⏸️ Remove original files only after extended verification
-2. ⏸️ Update documentation references
-3. ⏸️ Archive migration records
-4. ⏸️ Tag final migration commit
+**Phase 4: Cleanup** ✅ COMPLETE (December 16, 2025)
+1. ✅ Remove original files (29 files deleted)
+2. ✅ Update documentation references
+3. ✅ Archive migration records
+4. ✅ Tag final migration commit
 
-**Current State**: Main app now **exclusively uses capability location** for all JavaScript files. Templates updated: `document.html` and `edit-mode-fixed.html`. Both view and edit modes verified working. Original files remain in `/markitect/static/js/` for safety (can be removed in Phase 4). See `MIGRATION_STATUS.md` for verification results.
+**Final State**: Migration **fully complete**. Main app exclusively uses capability location. Legacy files removed. Single source of truth: `/capabilities/testdrive-jsui/js/`. All tests passing. See `MIGRATION_STATUS.md` for complete history.
 
 ## Common Development Tasks