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.

scripts/qa-radio.mjs

@@ -81,8 +81,6 @@ function check(name, ok, detail = '') {
 
 const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
 
-// Native pick buffers and clustered overlay entries settle on rendered frames,
-// not on wall-clock sleeps, particularly with software rendering.
 // Radio lives only inside Context; a user reaches its controls by expanding
 // Context and then Radio. Returns the prior collapse state so a step can put
 // the panels back for the scenarios that follow.
@@ -109,6 +107,8 @@ async function restoreRadioPanels(page, prior) {
   }, prior);
 }
 
+// Native pick buffers and clustered overlay entries settle on rendered frames,
+// not on wall-clock sleeps, particularly with software rendering.
 async function settleRadioFrames(page) {
   await page.evaluate(() => new Promise((resolve, reject) => {
     const scene = window.__godsEyeView.viewer.scene;