Phase 4 - Stream Health and Fallback:
- StreamHealthChecker with partial GET validation of m3u8 content
- Bitrate extraction from BANDWIDTH tags
- Response time measurement for quality ranking
- Fallback ordering: live first, fastest response time first
- GET /streams now only returns health-verified streams
Phase 5 - HLS Proxy Core:
- GET /proxy?url= - m3u8 playlist fetch with full URI rewriting
- GET /relay?url= - chunked segment relay (never buffers full segment)
- m3u8 rewriter handles master, variant, and segment URIs
- Base64url encoding for URL parameters
- CORS middleware for browser playback
- Range header forwarding for seeking support