chore: move feature list from TODO to BACKLOG and reorg admin/chat analytics items

.github/instructions/TODO.md

@@ -83,12 +83,3 @@ STREAMING.md contract vs playlist.go/main.ts implementation. See Backlog for ful
 - [x] Player error recovery: retries, backoff, reconnecting state (MEDIUM) — implemented: hls.on(ERROR) handler with exponential backoff
 - [x] Health endpoint: add active item, revision, run ID, segment info (LOW) — implemented: full STREAMING.md contract fields
 - [x] Phase 4 edge cache validation — script `scripts/validate-edge-cache.sh` created
-
-## Feature List (Future Enhancements)
-
-- [ ] Admin backend
-  - [ ] Analytics: implement a settings entry to set matomo url and page id
-- [ ] User frontend
-  - [ ] Chat: add user registration and login flows
-  - [ ] Chat: private DM history and search
-  - [ ] Analytics: add javascript snippet to send pageview events to matomo