feat(skills): author root SKILL.md for reference-curator suite + 7 sub-skills

Finish the migration for the dirs the bulk pass couldn't auto-handle:

- 90-reference-curator/SKILL.md: hand-authored suite orchestrator (pipeline overview,
  7-stage table, /reference-curator run modes, install) — the single loadable entry.
- 90-reference-curator/0{1..7}-*/SKILL.md: generated from each sub-skill's desktop/SKILL.md.
- scripts/migrate_skill_root.py: generalized discovery to find nested suite sub-skills
  (rglob desktop/code SKILL.md), so the migrator now handles suites too.

81-mac-optimizer, 91-multi-agent-guide, 94-dintel-bootstrap need NO root SKILL.md: they
are Claude Code plugins whose skill correctly lives at skills/<name>/SKILL.md (validated).
Adding a root SKILL.md there would violate plugin structure.

All SKILL.md repo-wide validate: flat-root=65, suite-sub=7, plugin-skills=3, 0 failures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom-skills/90-reference-curator/SKILL.md

@@ -0,0 +1,78 @@
+---
+name: 90-reference-curator
+description: |
+  Full reference-documentation curation pipeline: discover authoritative sources →
+  crawl → store → distill → quality-review (QA loop) → export to markdown / project files
+  / fine-tuning JSONL. A suite of 7 composable sub-skills with a single orchestrator entry.
+  Triggers: reference curator, curate documentation, build reference library, research
+  pipeline, discover sources, crawl docs, distill content, export reference, 레퍼런스 큐레이션,
+  문서 수집 파이프라인.
+version: "1.0"
+author: OurDigital
+environment: Code
+---
+
+# Reference Curator (90)
+
+A modular suite that turns a topic or a set of URLs into a curated reference library.
+Six stages run as a pipeline with a quality-review **QA loop**; each stage is also a
+standalone sub-skill you can run on its own.
+
+## Pipeline
+
+```
+discover → crawl → store → distill → review (QA loop) → export
+   01        02      03       04        05               06
+                         orchestrated by 07
+```
+
+| # | Sub-skill | Does | Root directive |
+|---|-----------|------|----------------|
+| 01 | reference-discovery | Find + credibility-rank authoritative sources | `01-reference-discovery/SKILL.md` |
+| 02 | web-crawler-orchestrator | Multi-backend crawl (Firecrawl / Node / aiohttp / Scrapy) | `02-web-crawler-orchestrator/SKILL.md` |
+| 03 | content-repository | MySQL storage with version tracking | `03-content-repository/SKILL.md` |
+| 04 | content-distiller | Summarize + extract key concepts | `04-content-distiller/SKILL.md` |
+| 05 | quality-reviewer | QA loop: approve / refactor / re-research routing | `05-quality-reviewer/SKILL.md` |
+| 06 | markdown-exporter | Export to markdown / project files / fine-tuning JSONL | `06-markdown-exporter/SKILL.md` |
+| 07 | pipeline-orchestrator | Coordinates all stages + QA loop + state | `07-pipeline-orchestrator/SKILL.md` |
+
+## How to run
+
+**Orchestrated (recommended)** — the `/reference-curator` command (see
+`commands/reference-curator-pipeline.md`):
+
+```bash
+# From a topic (starts at discovery)
+/reference-curator "Claude Code best practices" --max-sources 5
+
+# From URLs (skips discovery)
+/reference-curator https://docs.anthropic.com/en/docs/prompt-caching
+
+# Auto-approve + fine-tuning output
+/reference-curator "MCP servers" --auto-approve --export-format fine_tuning
+```
+
+Input modes: **topic** (→ discovery), **URLs** (→ crawl), **manifest** (→ resume).
+Key flags: `--depth light|standard|deep|full`, `--output`, `--max-sources`, `--max-pages`,
+`--auto-approve`, `--threshold`, `--max-iterations`, `--export-format project_files|fine_tuning|jsonl`.
+
+**Individual sub-skills** — each has a slash command in `commands/` and its own root
+`SKILL.md`; run any stage standalone (e.g. just discovery, or just export).
+
+## Install
+
+```bash
+cd custom-skills/90-reference-curator
+./install.sh            # interactive (storage dir, MySQL optional, crawler backend)
+./install.sh --minimal  # Firecrawl only, no MySQL
+./install.sh --check    # verify
+```
+
+Full guide: `USER-GUIDE.md`. Changelog: `CHANGELOG.md`.
+
+## Notes
+
+- Crawler backends and MySQL are optional — `--minimal` runs Firecrawl-only with no DB.
+- The QA loop (stage 05) gates quality before export; `--threshold` / `--max-iterations`
+  tune how strict and how many refinement passes per document.
+- This is a one-shot-per-topic curation workflow, not an always-on service.