fix(clip): a time's error line sits in the flow, the remove button off the cut, and every player surface rings amber

- useTimecodeField holds a time field's draft for its caller, which places TimecodeError (role
  alert) in its own flow under the fields' row: it no longer lies over the crop row taking its
  clicks, runs out of the editor's card, or joins the field's <label> name.
- The editor's remove-cut buttons sit in a row under the track at their cut (trackLeft), off the
  cut's grab area, where a press drags it; RangeTrack's adornment slot is gone.
- media-focus re-points --focus to the media amber on the Plex player, the YouTube stage and every
  bg-media-chrome surface; a contract test holds each such class string to media-focus or
  media-scope, the field's focus edge to the focus token, and --color-focus to the inline theme.
- An upload's quota headline says the converted file does not fit, not "Storage full".
- DESIGN.md: the tokens paragraph says what is re-pointed where; the decision row measures all
  three colours on the chrome.

frontend/src/index.css

@@ -145,6 +145,13 @@
   border-color: var(--edge-strong);
 }
 
+/* The focus ring on the always-dark player chrome (a player, its menus and panels): the media amber,
+   as a light theme's accent is dark (under 3:1 on the chrome). Every class string that paints
+   bg-media-chrome names it or media-scope (theme.contract.test.ts). */
+@utility media-focus {
+  --focus: var(--media-mark);
+}
+
 /* A form on the always-dark player chrome (the clip panel's fields): the neutral tokens the field
    primitives read are re-pointed to white-on-chrome for this subtree, so a light theme's dark text
    never lands on the dark bar. The accent stays the theme's for what is chosen; what must be seen