- Add aisbf/analytics.py module with Analytics class for tracking token usage,
  request counts, latency, error rates, and cost estimation per provider
- Add templates/dashboard/analytics.html with comprehensive dashboard page
- Integrate analytics recording into RequestHandler, RotationHandler, and
  AutoselectHandler
- Add /dashboard/analytics route in main.py
- Add Analytics link to base.html navigation
- Update CHANGELOG.md with new feature documentation

Features:
- Token usage tracking with database persistence
- Real-time request counts and latency tracking
- Error rates and types tracking
- Cost estimation per provider (Anthropic, OpenAI, Google, Kiro, OpenRouter)
- Model performance comparison
- Token usage over time visualization (1h, 6h, 24h, 7d)
- Optimization recommendations
- Export functionality (JSON, CSV)
- Integration with all request handlers
- Support for rotation_id and autoselect_id tracking