fix: APK update variant selection & Dolby Atmos stereo lossless fallback

[ajisth69]

Summary

1. Fix update APK selection: Dynamically downloads matching APK variant (universal.apk, universal-uncompressed.apk, or android7.apk) instead of always pulling the legacy Android 7 APK.
2. Fix Dolby Atmos fallback: When Dolby Atmos is selected but unavailable for a track, gracefully falls back to Stereo Lossless (Hi-Res / CD FLAC) instead of skipping to YouTube Music Opus.

Root Cause & Changes

1. APK Variant Selection

• In AppUpdateManager.kt, the release asset loop naively grabbed the first asset ending in .apk. Because GitHub releases list assets alphabetically, LastWave-v*-android7.apk was at index 0, so all users on Android 10+ standard and uncompressed releases were erroneously downloading the legacy Android 7.0 build.
• Added classifyAsset and selectBestAsset to properly match rawRelease (uncompressed), Android 7-9 (legacy), and Android 10+ (universal).

2. Dolby Atmos -> Stereo Lossless Fallback

• When Dolby Atmos (QUALITY_DOLBY_ATMOS = 28) was selected, if the track did not have a spatial audio mix on the addon, LosslessMusicApi.resolveStream returned null and triggered noteBackendFailure().
• After 2 misses, the backend cooldown (isCoolingDown) turned on, forcing the current track and all subsequent tracks directly to YouTube Music Opus.
• Fix: In LosslessMusicApi.kt and MusicPlayer.kt, when Dolby Atmos is not found, it seamlessly falls back to QUALITY_MAX_HI_RES (Stereo Hi-Res / CD FLAC) without triggering backend failure cooldown.