Fix multiple text tracks being selectable in the language menu

[MattiasBuelens]

Summary

Fixes #187: selecting a second subtitle track in <theoplayer-language-menu> did not deselect the first one, so multiple tracks were shown at the same time.

This worked in v1 and regressed in v2 with the introduction of RadioGroup.value (bc8188e). In v2, _onButtonChange only did this.value = button.value. Track buttons (TextTrackRadioButton, TextTrackOffRadioButton, MediaTrackRadioButton) do not set a value, so they all share undefined. The value setter returns early when the value is unchanged, and never unchecks the previously checked button.

Fix in RadioGroup:

 private readonly _onButtonChange = (event: Event) => {
     const button = event.target as RadioButton | null;
-    if (button !== null && button.checked) {
-        this.value = button.value;
-    }
+    if (button === null || !button.checked) return;
+    this._value = button.value;
+    this.setCheckedRadioButton(button);   // always uncheck the other buttons, like v1 did
+    this.dispatchEvent(createEvent('change', { bubbles: true }));
 };

 private updateCheckedButton(): void {
+    if (this._value === undefined) return;  // value-less buttons manage their own checked state
     ...
 }

The guard in updateCheckedButton() prevents find(b => b.value == undefined) from checking the first (e.g. "Off") button on slot change, which would otherwise disable a track that is showing by default.

Groups with explicit values (PlaybackRateRadioGroup, text track style menus) are unaffected: their value setter still drives updateCheckedButton().

Verification

• npm run test:format, test:typecheck, test:unit, build:debug pass.
• Verified in headless Chrome with examples/default-ui.html and a source with two WebVTT tracks (English, German): before the fix, clicking English then German left both tracks showing; after the fix only the last clicked track is showing, and "Off" disables both. A track with default: true stays selected on load.

Link to Devin session: https://dolby.devinenterprise.com/sessions/4a87b8e21d9344fc8c5e6a918b5ab471
Open in Devin Desktop: https://dolby.devinenterprise.com/desktop/session/4a87b8e21d9344fc8c5e6a918b5ab471?variant=devin
Requested by: @MattiasBuelens

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🦋 Changeset detected

Latest commit: 18d1f8a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@theoplayer/web-ui	Patch
@theoplayer/react-ui	Patch

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