Drop the Radio icon from Context and make the panel easier to read

The Context header carried a Radio icon that opened a second, compact
Radio player on top of the panel, duplicating the Radio section that
already lives inside Context. Remove the icon, the compact player and
everything that kept the two in step. Radio stays in Context as its own
section with one Enable control; Cockpit's compact Radio is unchanged.

Context itself was hard to read: 7-8 px labels at low contrast, a dashed
placeholder box, and a glow halo. The two modes are now one segmented
control, labels and guidance are 10 px at higher contrast, the standby
hint is plain text, section titles use --text-secondary, and the panel
draws no glow.

Unused translations are pruned, tests and QA harnesses that pinned the
compact player are updated or retired, and CURRENT-STATE and the
changelog describe the new header.

scripts/qa-firstrun-mutations.mjs

@@ -175,12 +175,12 @@ const MUTATIONS = [
     to: '    /* belt removed */',
   },
   {
-    // Anchored past the call so it cannot land on the cockpit disclosure's own
-    // stopImmediatePropagation() a few lines below and prove nothing about this.
-    defect: 'the radio disclosure returns to stopPropagation, so one ESC does two things',
+    // Anchored past the call so it lands on the Cockpit utility disclosure's
+    // Escape claim and nowhere else.
+    defect: 'a Cockpit utility disclosure returns to stopPropagation, so one ESC does two things',
     file: 'radio',
-    from: '      event.stopImmediatePropagation();\n      const escapedFromDisclosure =\n        event.target === this._contextRadioToggleBtn ||',
-    to: '      event.stopPropagation();\n      const escapedFromDisclosure =\n        event.target === this._contextRadioToggleBtn ||',
+    from: "      event.stopImmediatePropagation();\n      const kind = displayOpen ? 'display' : 'radio';",
+    to: "      event.stopPropagation();\n      const kind = displayOpen ? 'display' : 'radio';",
   },
   {
     defect: 'the "no timer" decision is deleted, so the next editor re-litigates it blind',