feat(reference-curator): Add portable skill suite for reference documentation curation

6 modular skills for curating, processing, and exporting reference docs:
- reference-discovery: Search and validate authoritative sources
- web-crawler-orchestrator: Multi-backend crawling (Firecrawl/Node/aiohttp/Scrapy)
- content-repository: MySQL storage with version tracking
- content-distiller: Summarization and key concept extraction
- quality-reviewer: QA loop with approve/refactor/research routing
- markdown-exporter: Structured output for Claude Projects or fine-tuning

Cross-machine installation support:
- Environment-based config (~/.reference-curator.env)
- Commands tracked in repo, symlinked during install
- install.sh with --minimal, --check, --uninstall modes
- Firecrawl MCP as default (always available)

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

custom-skills/90-reference-curator/commands/markdown-exporter.md

@@ -0,0 +1,138 @@
+---
+description: Export approved content to markdown files or JSONL for fine-tuning. Generates structured output with cross-references.
+argument-hint: <format> [--topic slug] [--min-score 0.80]
+allowed-tools: Read, Write, Bash, Glob, Grep
+---
+
+# Markdown Exporter
+
+Export approved content to structured formats.
+
+## Arguments
+- `<format>`: project_files | fine_tuning | knowledge_base
+- `--topic`: Filter by topic slug (e.g., "prompt-engineering")
+- `--min-score`: Minimum quality score (default: 0.80)
+
+## Export Formats
+
+### project_files (Claude Projects)
+
+Output structure:
+```
+~/reference-library/exports/
+├── INDEX.md                    # Master index
+└── {topic-slug}/
+    ├── _index.md               # Topic overview
+    ├── {document-1}.md
+    └── {document-2}.md
+```
+
+**INDEX.md format:**
+```markdown
+# Reference Library Index
+
+Generated: {timestamp}
+Total Documents: {count}
+
+## Topics
+
+### [Prompt Engineering](./prompt-engineering/)
+{count} documents | Last updated: {date}
+
+### [Claude Models](./claude-models/)
+{count} documents | Last updated: {date}
+```
+
+**Document format:**
+```markdown
+---
+source: {source_name}
+url: {original_url}
+credibility: {tier}
+quality_score: {score}
+exported: {timestamp}
+---
+
+# {title}
+
+{structured_content}
+
+## Related Documents
+- [Related Doc 1](./related-1.md)
+- [Related Doc 2](./related-2.md)
+```
+
+### fine_tuning (JSONL)
+
+Output: `~/reference-library/exports/fine_tuning_{timestamp}.jsonl`
+
+```json
+{"messages": [
+  {"role": "system", "content": "You are an expert on AI and prompt engineering."},
+  {"role": "user", "content": "Explain {topic}"},
+  {"role": "assistant", "content": "{structured_content}"}
+]}
+```
+
+### knowledge_base (Flat)
+
+Single consolidated file with table of contents.
+
+## Export Process
+
+### 1. Query Approved Content
+```sql
+SELECT dc.*, d.title, d.url, s.source_name, s.credibility_tier, t.topic_slug
+FROM distilled_content dc
+JOIN documents d ON dc.doc_id = d.doc_id
+JOIN sources s ON d.source_id = s.source_id
+LEFT JOIN document_topics dt ON d.doc_id = dt.doc_id
+LEFT JOIN topics t ON dt.topic_id = t.topic_id
+WHERE dc.review_status = 'approved'
+  AND (SELECT MAX(quality_score) FROM review_logs WHERE distill_id = dc.distill_id) >= ?;
+```
+
+### 2. Generate Cross-References
+
+Find related documents by:
+- Shared topics
+- Overlapping key concepts
+- Same source
+
+### 3. Write Files
+
+```bash
+mkdir -p ~/reference-library/exports/{topic-slug}
+```
+
+### 4. Log Export Job
+
+```sql
+INSERT INTO export_jobs
+  (export_name, export_type, output_format, topic_filter,
+   min_quality_score, output_path, total_documents, status)
+VALUES
+  (?, ?, ?, ?, ?, ?, ?, 'completed');
+```
+
+## Configuration
+
+From `~/.config/reference-curator/export_config.yaml`:
+```yaml
+output:
+  base_path: ~/reference-library/exports/
+  project_files:
+    structure: nested_by_topic
+    include_metadata: true
+quality:
+  min_score_for_export: 0.80
+  auto_approve_tier1_sources: true
+```
+
+## Example Usage
+
+```
+/markdown-exporter project_files
+/markdown-exporter fine_tuning --topic prompt-engineering
+/markdown-exporter project_files --min-score 0.90
+```