feat: add Buffer and Threshold sliders for Skip Silence on Android

[danieljrich]

Closes #364

Summary

Adds configurable Buffer (padding) and Threshold (dB cutoff) sliders when Skip Silence is enabled on Android.

Why

The default ExoPlayer 20 ms silence padding was cutting off word-initial unvoiced consonants (s, th, f, p) and trailing syllables on some audiobooks. Allowing users to adjust the buffer (0–200 ms, default 20 ms) and threshold (-50 to -20 dB, default -30 dB) resolves word clipping while keeping silence skipping fast and natural.

Key Changes

• Native Android pipeline: Slim wrapper (AbsorbSilenceAudioProcessor) delegating directly to Media3's SilenceSkippingAudioProcessor with on-the-fly parameter updates.
• Audio pipeline bridge: Static AbsorbSilenceController mirroring the established MonoController pattern.
• UI Sliders: Reuses _EffectRow in the Equalizer sheet with default position indicator tick marks:
  • Buffer: 0 ms – 200 ms (default: 20 ms)
  • Threshold: -50 dB – -20 dB (default: -30 dB)
• Persistence & Backup: Integrated into scoped preferences and backup/restore.

Testing

• Tested on Android with live run and release build.
• Verified slider adjustments immediately update audio playback in real-time.
• Verified per-book EQ overrides and reset button work as expected.

skip_silence_demo.mp4