fix: add verification gate before writing PROJECT.md in new-milestone

After gathering milestone goals and determining version, the workflow
now presents a summary and asks for confirmation before writing any
files. Users can adjust until satisfied, preventing the previous
behavior where GSD would immediately write PROJECT.md without verifying
its understanding of the milestone scope.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

get-shit-done/workflows/new-milestone.md

@@ -43,6 +43,38 @@ If the flag is absent, keep the current behavior of continuing phase numbering f
 - Suggest next version (v1.0 → v1.1, or v2.0 for major)
 - Confirm with user
 
+## 3.5. Verify Milestone Understanding
+
+Before writing any files, present a summary of what was gathered and ask for confirmation.
+
+```
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+ GSD ► MILESTONE SUMMARY
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+**Milestone v[X.Y]: [Name]**
+
+**Goal:** [One sentence]
+
+**Target features:**
+- [Feature 1]
+- [Feature 2]
+- [Feature 3]
+
+**Key context:** [Any important constraints, decisions, or notes from questioning]
+```
+
+AskUserQuestion:
+- header: "Confirm?"
+- question: "Does this capture what you want to build in this milestone?"
+- options:
+  - "Looks good" — Proceed to write PROJECT.md
+  - "Adjust" — Let me correct or add details
+
+**If "Adjust":** Ask what needs changing (plain text, NOT AskUserQuestion). Incorporate changes, re-present the summary. Loop until "Looks good" is selected.
+
+**If "Looks good":** Proceed to Step 4.
+
 ## 4. Update PROJECT.md
 
 Add/update: