feat: add EPUB TTS voice selection

[van-geaux]

Summary

• Add per-language EPUB Android TTS voice selection with device-specific compatible voice discovery and persistence.
• Distinguish voice variants in the selector and keep the list scrollable.
• Preserve the missing-language-data installation flow and keep EPUB 3 recorded narration separate.
• When a selected voice fails, clear that override, restore Default Android voice, preserve the reading locator, and reopen the player paused so the user can choose another voice or press Play.

Validation

• User confirmed the installed fallback behavior works on the connected Android device.
• :app:testDebugUnitTest
• :app:lintDebug
• :app:assembleDebug
• :app:assembleDebugAndroidTest
• Android-test Kotlin compilation
• CRLF-aware whitespace and UTF-8/mojibake checks

APK used for device validation:
/projects/bookorbit-android-issue-243/app/build/outputs/apk/debug/Lagrange-debug-202610082241.apk
SHA-256: 7c131fbc7cdce4f50a9c2b4235998f38cc8007e34949cb433581997903948f8e

Closes #243