Add initial Restreamer implementation for YouTube-to-Jellyfin live restreaming

PROJECT.md

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+# PROJECT.md
+
+## Goal
+
+A Docker container bundling Python, ffmpeg and yt-dlp that takes YouTube livestream URLs on one side and serves them
+as continuous, always-on streams on the other, consumable by Jellyfin Live TV via an M3U tuner. The service handles
+its own stream-session renewal so a channel does not die when YouTube's resolved URL expires after a few hours.
+
+## Current state
+
+Initial implementation in place:
+
+- `src/restreamer/` — resolver (yt-dlp), ffmpeg process wrapper, per-channel supervisor worker, broadcast fan-out,
+  aiohttp server (`/playlist.m3u`, `/stream/{channel_id}`, `/healthz`), config loading.
+- `serve.py` — entry point.
+- `Dockerfile` / `docker-compose.yml` — containerized deployment.
+- `channels.example.yaml`, `.env.example` — configuration templates.
+- Unit tests for the pure/testable pieces (config parsing, URL expiry parsing, ffmpeg argument building, playlist
+  generation, broadcast fan-out).
+
+Not yet done / not yet verified against a real YouTube livestream and a real Jellyfin instance — see `TODO`/`NOTE`
+comments in code for anything more granular.
+
+## Open questions
+
+- Whether channels also need XMLTV EPG data, or the bare M3U + `tvg-id` is enough for how Jellyfin is being used here.
+- Whether any of the YouTube URLs to restream require authentication (cookies) — `YtDlpResolver` accepts extra
+  `ydl_opts` for this but no cookie handling is wired up yet.