Move the changelog entry to changelog.d and clear review leftovers

The entry now lives in changelog.d/1471-context-panel-cleanup.md with
credit, as CONTRIBUTING asks, and CHANGELOG.md is back to main.

CURRENT-STATE no longer lists a compact Radio power control and scopes
the readability description to what Cyber keeps. The responsive glow
comment no longer cites the removed Radio popover, and qa-radio's
pick-buffer comment is back above settleRadioFrames.

Four test fixtures stop stubbing the removed launcher sync, and
PanelChrome drops the _syncRailPanelCollapseButton pass-through, wiring
the layout controller straight to _syncPanelCollapseButton.

src/ui/panelChrome.js

@@ -71,8 +71,7 @@ export class PanelChrome {
         variant: this.hud.getVariant(),
       }),
       scheduleCockpitLayout: () => this.cockpitView?.scheduleContextLayout(),
-      syncPanelCollapseButton: (panel) =>
-        this._syncRailPanelCollapseButton(panel),
+      syncPanelCollapseButton: (panel) => this._syncPanelCollapseButton(panel),
       readDisplayScrollTop: () =>
         this._displayPortalScrollRestoreOwner === 'standard'
           ? this._standardDisplayScrollTop
@@ -292,10 +291,6 @@ export class PanelChrome {
     return this._panelLayout._scheduleLeftPanelLayout(options0);
   }
 
-  _syncRailPanelCollapseButton(panelEl) {
-    this._syncPanelCollapseButton(panelEl);
-  }
-
   _syncPanelCollapseButton(panelEl) {
     const isRightRail = [
       'pp-toggles',