refactor: write-skill phase 1 refactor — grill, implementation, lessons

Complete 2026-05-18 workstream for write-skill refactor (issue 0018 phase 1).

Grill output (handoff in docs/issues/0018-factory-write-skill.md):
- 6-section standard replaces 8: Role and When/When not dropped (not in
  agentskills.io spec; description carries trigger scope and negatives)
- Frontmatter reduced to 3 fields; provenance moves to META.md
  (progressive disclosure — not loaded at every skill scan)
- SKILL-TEMPLATE.md and META-TEMPLATE.md as authoritative copy-fill artifacts
- CATEGORIES.md as self-contained category reference in skill directory
- Copy and fill explicitly split into separate process steps for determinism

New files in .agents/skills/write-skill/:
- SKILL-TEMPLATE.md — 6-section template with XML blocks and inline examples per section
- META-TEMPLATE.md — provenance schema with inline-commented YAML; source vs references explicit
- CATEGORIES.md — self-contained category table (no runtime dependency on factory docs)
- META.md — write-skill's own provenance (v1.1, self-authored)

SKILL.md rewritten: 8-step process, XML blocks (<requirements>, <steps>, <checks>),
3-field frontmatter, copy-then-fill steps explicit.

Supporting docs updated:
- skill-implementation-workflow.md: SKILL-TEMPLATE.md as authoritative template;
  source:/references: now reference META.md; when: marked resolved
- factory-integration-decisions.md: frontmatter spec corrected
- ROADMAP.md: authoring standard description updated
- CONTEXT.md: Source field entry corrected; META.md added to glossary
- docs/spec/overview.md: 2026-05-18 refactor entry added
- docs/issues/0018: handoff status updated; acceptance criteria marked complete

LESSONS.md: 3 entries added in grill session (cargo-culted body sections,
provenance fields in frontmatter, copy-fill determinism) + 1 from implementation
(planning meta-commentary does not belong in deployed artifacts).

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

docs/notes/factory-integration-decisions.md

@@ -53,7 +53,8 @@ All skills — new and rebuilt — must follow this standard:
 - `name:` — matches directory name
 - `description:` — trigger-tested before writing the body (explicit, implicit, negative cases)
 - `metadata: category:` — from the category table above
-- `metadata: version:` — semantic version; increment on meaningful changes
+
+`version:`, `updated:`, `when:`, `source:`, and `references:` are provenance/audit fields — they live in `META.md` alongside the SKILL.md (not in frontmatter). See `META-TEMPLATE.md` in `.agents/skills/write-skill/` for the META.md schema.
 
 **Body required sections:**
 - Constraints (highest-ROI element — prevents overengineering)