docs: rename Docker deployment to self-hosting guide with comprehensive monitoring documentation

Major documentation restructuring to emphasize self-hosting capabilities and fully document the real-time monitoring system.

Changes:
- Renamed docker-deployment.md → self-hosting.md to better reflect the value proposition
- Updated mkdocs.yml navigation to "Self-Hosting Guide"
- Completely rewrote introduction emphasizing self-hosting benefits:
  * Data privacy and ownership
  * Cost control and transparency
  * Performance and security advantages
  * Full customization capabilities

- Expanded "Metrics & Monitoring" → "Real-time Monitoring & Operations" with:
  * Monitoring Dashboard section documenting the /monitor UI
  * Complete feature breakdown (system health, requests, browsers, janitor, errors)
  * Monitor API Endpoints with all REST endpoints and examples
  * WebSocket Streaming integration guide with Python examples
  * Control Actions for manual browser management
  * Production Integration patterns (Prometheus, custom dashboards, alerting)
  * Key production metrics to track

- Enhanced summary section:
  * What users learned checklist
  * Why self-hosting matters
  * Clear next steps
  * Key resources with monitoring dashboard URL

The monitoring dashboard built 2-3 weeks ago is now fully documented and discoverable.
Users will understand they have complete operational visibility at http://localhost:11235/monitor
with real-time updates, browser pool management, and programmatic control via REST/WebSocket APIs.

This positions Crawl4AI as an enterprise-grade self-hosting solution with DevOps-level
monitoring capabilities, not just a Docker deployment.

Author: unclecode