test(a11y): cover delayed and interrupted Map Source focus

Keep the Esri settlement assertion exact, verify selected-source focus and Tab departure in Chromium, cancel pending work during disposal, and document the focused behavior.

src/ui.js

@@ -10167,6 +10167,7 @@ export class StyleManager {
     this._globalStatusNotice = null;
     if (this._globalLoadingStatus) this._globalLoadingStatus.hidden = true;
     this._disposed = true;
+    this._cancelMapSourceFocus?.();
     // Revoke persistence/hash authority before teardown can emit manager changes.
     this._layerStateCoordinator?.destroy();
     this._layerStateCoordinator = null;