Add screen reader support for language list

[rezabakhshilaktasaraei]

Summary

Exposes painted language rows in the language selection box as virtual accessibility children, making the list navigable by screen readers.

Changes (language_box.cpp)

• Overrides accessibilityChildCount(), accessibilityChildName(), accessibilityChildRect(), accessibilityChildState(), and accessibilityChildRole() on the inner widget.
• Each language row becomes a ListItem accessible child.
• Name format: native name + translated name (e.g. "Deutsch, German").
• Current language is reported with selected state.
• Fires accessibilityChildFocused() when selection changes via keyboard.
• Announces selected row on focusInEvent.

Dependencies

• Requires lib_ui#278 for Accessible::Item infrastructure.

No new lang keys

Uses only existing lng_* keys — no new strings added.

Test plan

• Open language selector (Settings → Language) with a screen reader
• Navigate rows with arrow keys — screen reader announces language names
• Verify the current language is reported as "selected"
• Verify hit-testing: clicking a row with screen reader cursor selects the correct language