fix(theme): R10 S1 review fixes — restore distinctions lost in the codemod

- PlexBrowse PLAYABLE_TINT: transcode was collapsed onto remux's bg-warn; give it
  bg-danger so direct/remux/transcode read as a distinct good->heavy green/amber/red
  gradient again.
- Live indicators (VideoCard row + thumbnail badge, playlistColumns badge): revert to
  fixed live-red + white instead of the --danger token. 'live' is a broadcast marker,
  not an error state, and the badge sits over a thumbnail (no app-bg contrast need);
  restores the conventional red/white LIVE look and decouples it from error retunes.
- ChannelPage exploring badge: drop the redundant dark:text-warn (no-op after the
  token rename — --warn is already theme-scoped).

error/fatal toast shade merge left as-is (both are 'bad'; the 400/500 step was subtle).

frontend/src/components/ChannelPage.tsx

@@ -325,7 +325,7 @@ export default function ChannelPage({
                 ) : (
                   ch?.explored &&
                   !ch?.subscribed && (
-                    <span className="text-xs px-2 py-0.5 rounded-full bg-warn/15 text-warn dark:text-warn">
+                    <span className="text-xs px-2 py-0.5 rounded-full bg-warn/15 text-warn">
                       {t("channel.exploringBadge")}
                     </span>
                   )