Cloudflare R2 mirror: bucket enable + Worker flip

## Что это Production R2 bucket с public read access, Worker route на `download.rox.one`, fallback на GH Releases если R2 down. Worker code готов в Phase 5b. ## Зачем GH Releases имеет rate limits и нестабилен для нагрузки релиза. R2 mirror = controlled bandwidth + analytics + предсказуемая latency на любом континенте. ## Источники вдохновения - [fatedier/frp](https://github.com/fatedier/frp) — mirror patterns - [linear/linear-release](https://github.com/linear/linear-release) — release dis ## 🔗 Linear - [PZD-246](https://linear.app/kuhjie/issue/PZD-246) (match confidence: 1.0)