Complete native rewrite: Kotlin, Jetpack Compose, and Media3 replace the old WebView app.

* New cockpit-style UI with CRT scanlines and four selectable colour themes (Phosphor, Amber, Ice, Mono)
* Gapless crossfade looping between segments
* True volume mute (layers keep running, silently)
* Settings to turn off individual visual effects (scanlines, spinner, VU flicker, glow, boot animation)

Known gap: the synthesised ambience sounds (deep-space drones, biome ambience) are being rebuilt for the new engine and are not included in this release. If you relied on those, hold off updating for now — more sounds are coming in follow-up releases.
