feat: Phase 3.3 — HLS manifest proxy with line-by-line rewriting
- HLSProxyService: rewrite_manifest() rewrites segment/sub-manifest/EXT-X-KEY URIs
to proxy URLs; proxy_segment() transparently proxies .ts segments
- Route: upstream status checked before streaming — 502 on failure
- CORS access-control-allow-origin: * on all responses
- Line rewriting: pass-through tags/comments, rewrite URIs, handle relative/absolute URLs
- URL resolution: urljoin for relative, absolute path, and absolute URL
- 22 tests (8 line rewriting, 4 URL resolution, 3 proxy URL construction,
2 manifest integration, 1 segment proxying, 4 route integration)
- 104/104 total pass (zero regressions)
3c9ed2cc8d