chore: remove obsolete DEVELOPMENT.md and consolidate task tracking docs

.github/instructions/BACKLOG.md

@@ -1,6 +1,15 @@
 # BACKLOG
 
-> Consolidated from `BACKLOG.md`, `DEVELOPMENT.md`, and `TODO.md` on 2026-08-11.
+## Remaining from 2026-08-11 (summary)
+
+- **Test Fixtures**: media + playlist fixtures created; ffmpeg generation commands documented in test headers
+- **User Frontend Tests**: video player, chat integration, responsive, accessibility, coverage
+- **Admin Frontend Tests**: playlist UI, moderation UI, metrics dashboards, coverage
+- **Cloudflare R2 Integration Test**: upload + cache header validation done (SyncToR2 with CacheControl + ContentType); edge cache hit/miss validation remains manual
+- **Cloudflare Config**: Cloudflare Pages deploy workflow and setup docs created; manual dashboard setup (Tiered Cache, WAF, rate limiting, HTTPS/HSTS) remains pending; Pages project must be created in dashboard first.
+- **External Services**: UptimeRobot monitors + alerts
+- **Production Deployment**: Hetzner provisioning, CD pipeline, DNS cutover, smoke test
+- **Scaling & Performance**: TTFB baseline and live benchmark runs still pending; loadtest scaffolding now includes Artillery/k6 helpers with auto summaries plus worksheet field mapping; chat p95, Redis saturation, and cache-hit threshold alerting are implemented
 
 ## Cloudflare Configuration