fix(clip): marks on the player chrome keep their amber in a light theme, and a removed cut hands the focus on

- A media amber (`--media-mark`), the same in both themes, for what marks a place on the always-dark
  chrome or over a video: the clip strip's playhead and focused end, the crop frame's ring, Plex's
  intro / credits markers. A light theme's warn was a dark amber there, under 3:1 (contract-tested).
- The editor's remove-cut button rings inside itself (the track clipped its ring), and once it goes
  with its cut the focus moves to the cut beside it, or to Split here, not to <body>.

frontend/src/components/ClipPanel.tsx

@@ -90,8 +90,9 @@ const LAST_MOMENT_S = 0.25;
 // On the always-dark chrome the ends are white (a light theme's accent is a dark blue there, which
 // all but vanished on the bar) and the playhead amber, so an end and the playhead are never confused.
 // A focused end is ringed in amber too, as the crop frame is: the accent ring was under 3:1 there.
-const PLAYHEAD = "bg-warn";
-const END_RING = "focus-visible:outline-warn";
+// The media amber (`--media-mark`), not the theme's warn: a light theme's is dark on this bar.
+const PLAYHEAD = "bg-media-mark";
+const END_RING = "focus-visible:outline-media-mark";
 
 export default function ClipPanel({
   src,