feat: Add NotebookLM skills (50-53) for Claude Code and Desktop

Add 4 specialized NotebookLM skills based on notebooklm-py library:

- 50-notebooklm-agent: Q&A agent for notebook queries with citations
- 51-notebooklm-automation: Full notebook/source/artifact management
- 52-notebooklm-studio: Content generation (podcasts, videos, quizzes)
- 53-notebooklm-research: Web/Drive research and source discovery

Each skill includes:
- README.md: Overview and quick start
- code/CLAUDE.md: Claude Code version (concise)
- desktop/SKILL.md: Claude Desktop version (with YAML frontmatter)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -0,0 +1,104 @@
+---
+name: 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 |