- Add ResponseCache class with multiple backend support (memory, Redis, SQLite, MySQL)
- Implement LRU eviction for memory backend with configurable max size
- Add SHA256-based cache key generation for request deduplication
- Implement TTL-based expiration (default: 600 seconds)
- Add cache statistics tracking (hits, misses, hit rate, evictions)
- Integrate caching into RequestHandler, RotationHandler, and AutoselectHandler
- Add granular cache control at model, provider, rotation, and autoselect levels
- Implement hierarchical configuration: Model > Provider > Rotation > Autoselect > Global
- Add dashboard endpoints for cache statistics (/dashboard/response-cache/stats) and clearing (/dashboard/response-cache/clear)
- Add response cache initialization in main.py startup event
- Skip caching for streaming requests
- Add comprehensive test suite (test_response_cache.py) with 6 test scenarios
- Update configuration models with enable_response_cache fields
- Update TODO.md to mark Response Caching as completed
- Update CHANGELOG.md with response caching features

Files created:
- aisbf/response_cache.py (740+ lines)
- test_response_cache.py (comprehensive test suite)

Files modified:
- aisbf/handlers.py (cache integration and _should_cache_response helper)
- aisbf/config.py (ResponseCacheConfig and enable_response_cache fields)
- config/aisbf.json (response_cache configuration section)
- main.py (response cache initialization)
- TODO.md (mark task as completed)
- CHANGELOG.md (document new features)