feat(skills): bulk-add root SKILL.md to 61 skills (native Agent Skills loadability)

Run the additive migration pass from SKILL-MIGRATION-GUIDE: generate a root SKILL.md
for every skill that lacked one, copied from its desktop/SKILL.md (or code/SKILL.md),
with name set to the directory name and description + body preserved verbatim.

- scripts/migrate_skill_root.py: the reusable, non-destructive migrator (dry-run default).
- 61 new root SKILL.md (desktop source for most; code/SKILL.md for 61/62/92).
- Untouched: 16/17/95 (already had root); desktop/ and code/ packaging left intact.
- All 64 root SKILL.md validate: frontmatter <=1024, kebab name, description present.

Still MANUAL (no SKILL.md source — commands/README only), need hand-authored root SKILL.md:
81-mac-optimizer, 90-reference-curator, 91-multi-agent-guide, 94-dintel-bootstrap.

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

custom-skills/51-notebooklm-automation/SKILL.md

@@ -0,0 +1,104 @@
+---
+name: 51-notebooklm-automation
+description: |
+  Complete NotebookLM automation for notebooks, sources, and artifacts management.
+  Triggers: manage NotebookLM, create notebook, add sources, 노트북 관리, NotebookLM 자동화.
+---
+
+# NotebookLM Automation
+
+Complete programmatic control over NotebookLM notebooks, sources, and artifacts.
+
+## Prerequisites
+
+```bash
+pip install notebooklm-py
+playwright install chromium
+notebooklm login
+```
+
+## When This Skill Activates
+
+- "Create a NotebookLM notebook"
+- "Add sources to NotebookLM"
+- "Manage my notebooks"
+- Korean: "노트북 만들어줘", "소스 추가"
+
+## Quick Reference
+
+### Notebook Operations
+
+| Task | Command |
+|------|---------|
+| List all | `notebooklm list` |
+| List (JSON) | `notebooklm list --json` |
+| Create | `notebooklm create "Title"` |
+| Rename | `notebooklm rename <id> "New"` |
+| Delete | `notebooklm delete <id>` |
+| Set context | `notebooklm use <id>` |
+
+### Source Operations
+
+| Task | Command |
+|------|---------|
+| Add URL | `notebooklm source add "https://..."` |
+| Add file | `notebooklm source add ./file.pdf` |
+| Add YouTube | `notebooklm source add "youtube.com/..."` |
+| List sources | `notebooklm source list` |
+| Delete source | `notebooklm source delete <id>` |
+| Wait for ready | `notebooklm source wait <id>` |
+
+### Artifact Operations
+
+| Task | Command |
+|------|---------|
+| List artifacts | `notebooklm artifact list` |
+| Wait for completion | `notebooklm artifact wait <id>` |
+| Delete artifact | `notebooklm artifact delete <id>` |
+
+## Workflows
+
+### Bulk Import Sources
+
+```bash
+notebooklm create "Research Collection"
+notebooklm source add "https://url1.com"
+notebooklm source add "https://url2.com"
+notebooklm source add ./local.pdf
+notebooklm source list
+```
+
+### CI/CD Integration
+
+Use `--json` for machine-readable output:
+
+```bash
+# Create and capture ID
+NOTEBOOK_ID=$(notebooklm create "Docs" --json | jq -r '.id')
+
+# Add sources
+notebooklm source add "https://docs.example.com" --json
+
+# Export for downstream processing
+notebooklm list --json > notebooks.json
+```
+
+## Environment Variables
+
+| Variable | Purpose |
+|----------|---------|
+| `NOTEBOOKLM_HOME` | Custom config directory |
+| `NOTEBOOKLM_AUTH_JSON` | Inline auth (CI/CD) |
+
+## Autonomy Rules
+
+**Auto-run:** `list`, `status`, `source list`, `artifact list`, `create`, `use`
+**Ask first:** `delete`, `rename`
+
+## Error Handling
+
+| Error | Solution |
+|-------|----------|
+| Auth error | `notebooklm login` |
+| No context | `notebooklm use <id>` |
+| Rate limit | Wait 5-10 min, retry |