fix(player): keep capture dialog dismissible via outside tap

[TsangAsuna]

Summary

• On tablet-like mobile devices during fullscreen playback (control bar hidden), the media capture dialog (opened by tapping or long-pressing the screenshot button) disabled barrier dismissal, leaving the top-right close button as the only way to close the dialog.
• Pass barrierDismissible: true unconditionally so tapping outside the dialog closes it, consistent with other Nipaplay windows: the desktop NipaplayWindowScaffold background tap handler and the phone bottom sheet barrier already support outside-tap dismissal.

What Changed

• lib/pages/play_video_page.dart: _showMediaCaptureSettings now always passes barrierDismissible: true to showMediaCaptureDialog instead of gating on _shouldDisableDialogDismiss.

Verification

• flutter analyze --no-fatal-infos --no-fatal-warnings lib/pages/play_video_page.dart: no new issues (3 pre-existing info-level hints in untouched code).
• flutter test --no-pub test/media_capture_dialog_input_test.dart: 3/3 passed.

[FurudeRika123]

Reviewed the change.

Passing barrierDismissible: true unconditionally for the media capture dialog keeps outside-tap dismissal consistent with the other dialogs on this page, and _shouldDisableDialogDismiss() stays in use by _showAirPlayPicker(), so the helper is not left dead. Change is small and scoped; LGTM.

One note for the record: Analyze and Test is currently red on this head SHA, but the failure is test/television_media_library_test.dart: media collection restores each source sort after switching sections, which also fails on unrelated PRs — it is not caused by this diff.