fix(tuner): anchor injectPlayerButton to a direct-child button (feedBack#800)

`injectPlayerButton()` anchored the injected Tuner button with
`controls.querySelector('button:last-child')`, which can match a NESTED
button that is not a direct child of `#player-controls`. `insertBefore(btn,
nestedButton)` then throws `NotFoundError` (the reference node must be a
direct child); since injection runs from the tuner's `screen:changed`
handler, the throw propagated out of the player-screen transition and
stalled its render. The v3 path was already safe (plugin-control slot);
only the classic anchor was bad.

Use `:scope > button:last-of-type` (direct child only) with a
`parentNode === controls` guard before insertBefore, falling back to
appendChild. Bump plugins/tuner 1.3.3 → 1.3.4.

Test: tests/plugins/tuner/js/inject_player_button.test.js — extracts the
real function and runs it over a faithful DOM model whose insertBefore
enforces the direct-child invariant; the nested-last-button case reproduces
the throw on the old anchor and passes on the new one (5 tests).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: byrongamatos <xasiklas@gmail.com>

plugins/tuner/plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "tuner",
   "name": "Guitar/Bass Tuner",
-  "version": "1.3.3",
+  "version": "1.3.4",
   "bundled": true,
   "private": false,
   "script": "screen.js",

plugins/tuner/utils/ui.js

@@ -869,8 +869,15 @@ window._tunerUI = function(state, actions) {
         btn.textContent = 'Tuner';
         btn.title = 'Open Tuner';
         btn.onclick = window.tuner.toggle;
-        const closeBtn = isV3 ? null : controls.querySelector('button:last-child');
-        if (closeBtn) controls.insertBefore(btn, closeBtn);
+        // Anchor to the last DIRECT-child button of `controls` (the classic
+        // transport's close/exit button). A bare `button:last-child` can match
+        // a NESTED button that is not a direct child of `controls`, and
+        // `insertBefore()` then throws NotFoundError — which propagated out of
+        // the player-screen transition and aborted its render (feedBack#800).
+        // `:scope > button:last-of-type` restricts the anchor to a direct child;
+        // the parentNode check is a belt-and-suspenders guard before insertBefore.
+        const closeBtn = isV3 ? null : controls.querySelector(':scope > button:last-of-type');
+        if (closeBtn && closeBtn.parentNode === controls) controls.insertBefore(btn, closeBtn);
         else controls.appendChild(btn);
         updatePlayerButton();
     }