The in-app IFrame player showed YouTube's bare 'Video unavailable' screen
with no way out when a video couldn't be embedded (auto-generated Topic
art-tracks disable embedding -> error 101/150; removed/private -> 100).
Catch the IFrame onError and overlay a clear message + 'Open on YouTube'
button, with a tailored note for embedding-disabled videos.
PlayerModal now accepts an optional queue + startIndex. The active item drives the
player; it recreates per item (reusing the single-video resume / auto-watch / progress
logic), auto-advances to the next item when one ends, and shows Previous / Next controls
with an N / M indicator. The Playlists page passes the playlist as the queue from Play all
or a clicked row. Trilingual previous/next strings.
Feed, VideoCard, Sidebar, PlayerModal, Channels, Stats, SettingsPanel,
OnboardingWizard, NotificationCenter, Toaster, ErrorBoundary and the relativeTime
helper are now fully translated in Hungarian, English and German, each with its own
locale area file (auto-loaded). Key parity verified across all three languages.
