docs: Chunk 3 grill, PRD, ADRs, and doc updates

- docs/prd/chunk-3-skills-library.md: PRD for 42-skill library rebuild;
  AGENTS.md refactor as prerequisite; factory bootstrap order (write-eval
  first); source field schema; upstream review cadence; design phase
  sequence; IaC/Gitea scope decisions
- docs/adr/0011-provider-agnostic-issue-tracker.md: file-based default,
  Gitea as provider adapter, "issue" as canonical cross-provider term
- docs/adr/0012-agents-md-provider-agnostic-entry-point.md: AGENTS.md as
  content source, CLAUDE.md as thin adapter; partially supersedes ADR-0005
- CONTEXT.md: 8 new glossary terms (AGENTS.md, skill composition, source
  field, provider-agnostic issue tracker, design phase sequence, PRD scope,
  issue scope, bidirectional reference principle); CLAUDE.md index model
  updated; stale workflow example fixed
- docs/ROADMAP.md: changelog tooling and IaC/Gitea scope resolved; when:
  field question updated; Chunk 3 grill housekeeping note added
- docs/spec/overview.md: Chunk 3 target updated with PRD link, skill count,
  and AGENTS.md prerequisite

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

docs/spec/overview.md

@@ -11,7 +11,9 @@ Current deployed state of this repo — what you get if you run `install.sh` tod
 
 Current skills: `caveman`, `diagnose`, `grill-me`, `grill-with-docs`, `improve-codebase-architecture`, `prototype`, `tdd`, `to-issues`, `to-prd`, `triage`, `write-a-skill`, `zoom-out`.
 
-**Chunk 3 target:** the full skill library defined in `docs/research/ai-coding-factory/ai-coding-factory-skills-index.md`. That file is the canonical build reference — trigger descriptions, constraints, and category for each skill. Skills are stored flat (`skill-name/SKILL.md`) per ADR-0009; the `category/skill-name` notation in the skills-index is for identification only. Core categories: roles, design, factory, implement, test, review, deploy, operate, cross-cutting. Global optional: iac, gitea. Delete the skills-index once all skills exist.
+**Chunk 3 target:** 42 skills across 9 categories. PRD: `docs/prd/chunk-3-skills-library.md`. Canonical build reference: `docs/research/ai-coding-factory/ai-coding-factory-skills-index.md` (delete once all skills exist). Skills stored flat (`skill-name/SKILL.md`) per ADR-0009; category in `metadata.category` frontmatter. Categories: design, factory, implement, test, review, deploy, operate, cross-cutting, iac (2 skills only — docker-compose + iac-security-review). Role skills (6) deferred to Chunk 5. Gitea skills moved to `providers/gitea/` provider adapter.
+
+**Prerequisite:** AGENTS.md refactor must complete before Chunk 3 skill implementation begins — both `CLAUDE.md` files (repo-level and global) become thin adapters importing `AGENTS.md`. See ADR-0012 (to be written during implementation).
 
 ### Claude Code configuration
 - `~/.claude/CLAUDE.md` — global config index; always-on rules + content index pointers