Add subtitle regex filters

[1Selxo]

Summary

• add a Regex button to the subtitles sheet with preset subtitle text filters and custom regex support
• keep raw subtitle cues separately and expose filtered text as the effective subtitle text
• refresh the subtitle list, active cue, and lookup text when regex filters change

Test

• .\gradlew.bat :app:compileDebugKotlin --console=plain
• git diff --check

Note: broader Spotless checks currently fail on pre-existing unrelated formatting issues in upstream files.