feat(playout): replace time-based R2 retention with run-count and size caps

docs/STREAMING.md

@@ -180,6 +180,8 @@ A release is streaming-ready only when one full playlist boundary has played wit
 | `R2_ENDPOINT`, `R2_REGION`                 | S3-compatible publication endpoint                 |
 | `R2_BUCKET_NAME`                           | Media bucket                                       |
 | `R2_ACCESS_KEY_ID`, `R2_SECRET_ACCESS_KEY` | Write credentials, available only to the publisher |
+| `R2_KEEP_RUNS`                             | Number of run folders to retain (default `2`)      |
+| `R2_MAX_RETENTION_BYTES`                   | Max bytes retained across run folders (10 GiB)     |
 | `MEDIA_DOMAIN`                             | Public R2 custom domain                            |
 | `VITE_PUBLIC_HLS_URL`                      | Public live manifest URL                           |