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/shared/config/db_config.yaml

@@ -0,0 +1,31 @@
+# Reference Curator - Database Configuration
+# Location: ~/.config/reference-curator/db_config.yaml
+#
+# Environment variables (set in ~/.reference-curator.env):
+#   MYSQL_USER     - MySQL username (required)
+#   MYSQL_PASSWORD - MySQL password (required)
+#   MYSQL_HOST     - MySQL host (optional, default: localhost)
+#   MYSQL_PORT     - MySQL port (optional, default: 3306)
+
+mysql:
+  host: ${MYSQL_HOST:-localhost}
+  port: ${MYSQL_PORT:-3306}
+  database: reference_library
+  user: ${MYSQL_USER}
+  password: ${MYSQL_PASSWORD}
+  charset: utf8mb4
+
+  # Connection pool settings
+  pool_size: 5
+  pool_recycle: 3600
+
+  # SSL (if needed for remote MySQL)
+  ssl:
+    enabled: false
+    ca_cert: null
+
+# Backup settings
+backup:
+  enabled: true
+  path: ${REFERENCE_LIBRARY_PATH:-~/reference-library}/backups/
+  retention_days: 30