Fix subtitle appearance persistence and bump to 3.3.8

[kalzEOS]

Summary

• fix subtitle appearance defaults so the app no longer falls back to stale TV caption styling
• keep subtitle appearance dialog changes dirty until applied so APPLY activates and saves correctly
• bump the app to 3.3.8 and enforce tag-to-build version matching in release validation

Verification

• GRADLE_USER_HOME=/tmp/gradle ./gradlew :app:testDebugUnitTest --tests com.example.xtreamplayer.settings.SubtitleAppearanceSettingsTest
• GRADLE_USER_HOME=/tmp/gradle ./gradlew :app:compileDebugKotlin
• bash scripts/validate_release_metadata.sh XtreamPlayerv3.3.8 'Xtream Player v3.3.8' <notes-file> false main