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

.github/MEMORY.md

@@ -138,7 +138,7 @@
 ## 2026-08-13
 
 - Completed all remaining enhancement tasks (only manual/infrastructure phases left):
-  - **Playout**: automatic media normalization on upload (`media.NormalizeVideo`, `*.normalized.mp4`, statuses `ready`/`needs_normalization`/`normalizing`/`normalization_failed`, `POST /api/admin/media/{id}/normalize`); R2 segment retention (`cleanupOldSegments`, `R2_SEGMENT_RETENTION_HOURS`); seamless looping (playlist SHA-256 fingerprint + `-start_number`); single `start-playout.sh` entrypoint + `-validate` mode; loop/cleanup metrics.
+  - **Playout**: automatic media normalization on upload (`media.NormalizeVideo`, `*.normalized.mp4`, statuses `ready`/`needs_normalization`/`normalizing`/`normalization_failed`, `POST /api/admin/media/{id}/normalize`); R2 segment retention (`cleanupOldRuns`, keep last `R2_KEEP_RUNS` runs, `R2_MAX_RETENTION_BYTES` cap); seamless looping (playlist SHA-256 fingerprint + `-start_number`); single `start-playout.sh` entrypoint + `-validate` mode; loop/cleanup metrics.
   - **Application configuration**: thread-safe JSON runtime config store (`backend/chat/src/config/runtime.go`) shared with playout via `/app/playlist/config.json`; `GET/PUT /api/admin/config`; admin UI config form.
   - **Matomo analytics**: public `GET /api/matomo` + viewer pageview snippet in `index.html`.
   - **Chat user accounts**: register/login/logout/session endpoints, bcrypt hashing, `linearvoid_user_session` cookie, viewer sign-in UI.

.github/instructions/TODO.md

@@ -2,10 +2,6 @@
 
 > Completed tasks moved to [DONE](./DONE.md). Remaining tasks in [BACKLOG](./BACKLOG.md).
 
-## R2 Data Retention
-
-- [ ] Adjust internal data retention for R2: remove folders /hls/r-{ISOTIME} after next run, keep only the last 2 runs or max. 10GB of data
-
 ## Frontend Tests
 
 ### User Frontend