refactor: reorganize template write paths + add frontmatter + manifest

All skill templates now write artifacts to subdirectories under
$PROJECTS_DIR/$SLUG/ (reviews/, plans/, reports/). Adds YAML
frontmatter to markdown artifacts and manifest-append calls.

Templates updated:
- plan-eng-review: plans/ + reviews/
- plan-ceo-review: plans/ceo/ + reviews/
- plan-design-review: reviews/
- ship: reviews/
- design-review: reports/
- qa: reports/
- qa-only: reports/
- review/greptile-triage: uses gstack-slug instead of remote-slug

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

design-review/SKILL.md.tmpl

@@ -207,11 +207,29 @@ Write the report to both local and project-scoped locations:
 **Local:** `.gstack/design-reports/design-audit-{domain}-{YYYY-MM-DD}.md`
 
 **Project-scoped:**
+
+{{ARTIFACT_SETUP}}
+
 ```bash
-eval $(~/.claude/skills/gstack/bin/gstack-slug 2>/dev/null)
-mkdir -p ~/.gstack/projects/$SLUG
+mkdir -p $PROJECTS_DIR/$SLUG/reports
+FILE="$PROJECTS_DIR/$SLUG/reports/design-{domain}-$DATE.md"
+[ -f "$FILE" ] && FILE="$PROJECTS_DIR/$SLUG/reports/design-{domain}-$DATE-$(date +%H%M).md"
+```
+
+Write to the file path resolved above. Include YAML frontmatter:
+```yaml
+---
+type: design-audit
+branch: {branch}
+date: {YYYY-MM-DD}
+skill: design-review
+---
+```
+
+After writing, register in manifest:
+```bash
+~/.claude/skills/gstack/bin/gstack-manifest-append design-audit "reports/$(basename "$FILE")" design-review "$BRANCH"
 ```
-Write to `~/.gstack/projects/{slug}/{user}-{branch}-design-audit-{datetime}.md`
 
 **Per-finding additions** (beyond standard design audit report):
 - Fix Status: verified / best-effort / reverted / deferred