Update implementation guide - Phase 4 complete

Mark Phase 4 (stack removal detection) as complete in the
implementation guide checklist and status section.

Workflow now reduced to 1,392 lines (down from original 2,548).

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: owine

scripts/deployment/IMPLEMENTATION_GUIDE.md

@@ -1,10 +1,11 @@
 # Deployment Script Extraction - Implementation Guide
 
-## Status: Phase 3 Complete ✅
+## Status: Phase 4 Complete ✅
 
 - Phase 1: Foundation library created and committed (b2effaa, 41a80ed)
 - Phase 2: Health check extraction complete (f6ae6d1, c60ce75) - EXPRESSION LIMIT FIXED ✅
-- Phase 3: Deployment extraction complete (63871ac) - Further workflow simplification ✅
+- Phase 3: Deployment extraction complete (63871ac, 72cd05f) - Further workflow simplification ✅
+- Phase 4: Stack removal detection complete (15a1cc0) - Modular detection and cleanup ✅
 
 ## Problem Statement
 
@@ -341,7 +342,7 @@ To continue this refactor:
 - [x] Phase 1: Library infrastructure
 - [x] Phase 2: Health check extraction ✅ **EXPRESSION LIMIT FIXED**
 - [x] Phase 3: Deployment extraction ✅ **WORKFLOW SIMPLIFIED**
-- [ ] Phase 4: Stack removal extraction
+- [x] Phase 4: Stack removal extraction ✅ **MODULAR DETECTION**
 - [ ] Phase 5: Rollback extraction
 - [ ] Phase 6: Cleanup and validation