fix(player): what is chosen on the player chrome is marked amber, not written in the accent

A light theme's accent as text on the always-dark chrome was 2.84:1 (Slate). `--chosen` is the
accent unless a scope names its own; `media-marks` (was media-focus) points it, with the focus
ring, at the media amber. A chosen track stays white with an amber tick (MenuCheck reads
`text-chosen`); a chosen settings tab or toggle is white with an amber underline (MEDIA_CHOSEN).
The theme contract test holds the token, the tick and the player components free of accent text.

frontend/src/components/ui/Tabs.tsx

@@ -2,6 +2,7 @@ import { Fragment, useId, useRef, type KeyboardEvent } from "react";
 import { panelId, tabId } from "./tabPanel";
 import { type LucideIcon } from "lucide-react";
 import CountBadge from "./CountBadge";
+import { MEDIA_CHOSEN } from "./mediaChrome";
 
 // Reusable pill tab-rail for in-page sub-navigation (Configuration, Users & roles, the Settings
 // sections, the Stats overview/system split…). Horizontal by default; `orientation="vertical"` gives
@@ -125,7 +126,7 @@ export default function Tabs({
               className={
                 tone === "media"
                   ? `touch-target flex-1 items-center justify-center whitespace-nowrap rounded px-2 py-1 text-2xs ${
-                      on ? "bg-white/15 text-accent" : "text-white/70 hover:bg-white/10"
+                      on ? MEDIA_CHOSEN : "text-white/70 hover:bg-white/10"
                     }`
                   : `pill touch-target items-center rounded-lg px-3 text-sm ${
                       vertical