fix: write-skill governance review — model field, eval self-check, grill wiring

- Add model: sonnet to SKILL.md frontmatter (Claude Code extension; correct
  location per research — runtime config belongs in frontmatter, not META.md)
- Document model field in SKILL-TEMPLATE.md with factory §9 routing guidance
- Wire grill output explicitly to trigger description step (step 3 now references
  agreed name/category/purpose from grill rather than drafting independently)
- Strengthen eval self-check: presence check → coverage check (trigger cases +
  at least one output case required)
- Bump META.md to v1.2 (2026-05-26)
- Add three LESSONS.md entries: META-TEMPLATE comment retention, overlap check
  scope (deployed dir not just repo), model field placement boundary

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

.agents/skills/write-skill/SKILL-TEMPLATE.md

@@ -11,6 +11,9 @@ description: <trigger description>
 metadata:
   category: <category — see CATEGORIES.md>
 # allowed-tools: <add only when the skill has a narrow, well-defined tool surface; omit otherwise>
+# model: sonnet | opus | haiku — Claude Code extension; overrides session model for this skill's turn.
+# Omit to inherit the active session model. Factory §9 routing: haiku=formatting/classification,
+# sonnet=most coding/review, opus=adversarial/complex reasoning.
 ---
 
 <requirements>