feat: add scope drift to /ship, extract from /review template

/ship gets {{SCOPE_DRIFT}} at Step 3.48 + PR body slot. /review replaces
hardcoded scope drift with {{SCOPE_DRIFT}} + {{PLAN_COMPLETION_AUDIT_REVIEW}}.

ship/SKILL.md.tmpl

@@ -232,6 +232,8 @@ If multiple suites need to run, run them sequentially (each needs a test lane).
 
 {{LEARNINGS_SEARCH}}
 
+{{SCOPE_DRIFT}}
+
 ---
 
 ## Step 3.5: Pre-Landing Review
@@ -509,6 +511,10 @@ you missed it.>
 <If no Greptile comments found: "No Greptile comments.">
 <If no PR existed during Step 3.75: omit this section entirely>
 
+## Scope Drift
+<If scope drift ran: "Scope Check: CLEAN" or list of drift/creep findings>
+<If no scope drift: omit this section>
+
 ## Plan Completion
 <If plan file found: completion checklist summary from Step 3.45>
 <If no plan file: "No plan file detected.">