Include PLAN.md in phase completion commits

Preserve the execution plan alongside SUMMARY.md in git history.

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

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

get-shit-done/workflows/execute-phase.md

@@ -1118,6 +1118,7 @@ NEVER use:
 **1. Stage planning artifacts:**
 
 ```bash
+git add .planning/phases/XX-name/{phase}-{plan}-PLAN.md
 git add .planning/phases/XX-name/{phase}-{plan}-SUMMARY.md
 git add .planning/STATE.md
 ```