feat: add sort options to Downloads screen

[lesquel]

Summary

Add the ability to sort downloaded songs by multiple criteria with ascending/descending direction. The sort preference persists between sessions.

Sort Options

Option	Description
Newest first	Download date, most recent first (default — current behavior)
Oldest first	Download date, oldest first
Title (A-Z)	Alphabetical by song title
Title (Z-A)	Reverse alphabetical by song title
Artist (A-Z)	Alphabetical by artist name
Artist (Z-A)	Reverse alphabetical by artist name

Implementation Details

Architecture

• No changes to core submodule — all new code lives in composeApp
• Follows the same MVVM + StateFlow + Compose patterns used throughout the app
• Reuses the visual style of SortPlaylistBottomSheet from LocalPlaylistScreen

New Files

• DownloadSortType.kt — Sealed class with 6 sort variants + serialization (toKey()/fromKey())

Modified Files

• LibraryDynamicPlaylistViewModel.kt — Reactive sorting via combine(rawSongs, sortType), preference persistence via DataStoreManager.putString()/getString()
• LibraryDynamicPlaylistScreen.kt — Sort icon button in TopAppBar (visible only for Downloaded type), SortDownloadsBottomSheet integration
• ModalBottomSheet.kt — New SortDownloadsBottomSheet composable
• AllExt.kt — DownloadSortType.displayNameRes() extension function
• 26 strings.xml files — i18n support for all existing locales (ar, az, bg, ca, de, es, fa, fi, fr, hi, in, it, iw, ja, ko, nl, pl, pt, ru, th, tr, uk, vi, zh, zh-rTW)

Key Design Decisions

• DownloadSortType is separate from FilterState (avoids modifying core submodule)
• DataStoreManager injected via by inject() from KoinComponent (no DI module changes needed)
• Client-side sorting (in-memory) — appropriate for typical download list sizes
• Sort preference key: "download_sort_type"

Screenshots

Sort icon appears in the Downloads screen TopAppBar. Tapping opens a bottom sheet with 6 sort options.

Testing Checklist

• Navigate to Library → Downloaded → sort icon is visible
• Each sort option reorders the list correctly
• Sort preference persists after leaving and returning to the screen
• Search works correctly with any active sort order
• Empty download list doesn't crash
• Songs without artist name sort correctly (fallback to empty string)