Adds a "Proxy videos" toggle in instance settings that routes video
streams through the instance instead of connecting directly to YouTube
CDN. Includes auto-detection of 403 blocks and live re-application of
proxy settings without requiring app restart or video reload.
Shows an orange "DEV" capsule next to the iCloud row in Settings and a
development environment notice at the top of iCloud settings, helping
distinguish CloudKit dev environment from production during development.
