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.
Use URLComponents/URLQueryItem for standard form-URL encoding instead
of manual percent-encoding with CharacterSet.alphanumerics, which
included non-ASCII Unicode letters and had an unsafe raw-value fallback.
Playlists only loaded the first page of videos. Add full pagination for
both Invidious and Piped playlist endpoints (public and authenticated).
Deduplicate Invidious results by playlist index to handle its overlapping
page windows. Also fix URL encoding in Invidious login to use strict
form-encoding charset.
