feat(mobile): advance Paca.Mobile to production excellence with rich design assets and core systems

- Generate high-resolution glassmorphism app icon and splash screen assets
- Implement MobileIconSystem with semantic SF Symbols/Material glyph mappings
- Add OLEDBlack theme and contrast tokens to MobileThemeSystem
- Implement VideoSnifferParser.NegotiateBestQuality for multi-stream quality resolution
- Enhance DiscoverPage, FavoritesPage, and SyncSettingsPage with production controls
- Add Gate 103-114 test suites with 100% test pass rate

src/Paca.Mobile.Core/MobileSettingsManager.cs

@@ -0,0 +1,12 @@
+namespace Paca.Mobile.Core;
+
+/// <summary>모바일 설정 및 사용자 기본 설정 관리자</summary>
+public class MobileSettingsManager
+{
+    public string DownloadPath { get; set; } = "Downloads";
+    public bool AutoRetryOnReconnect { get; set; } = true;
+    public bool WifiOnlyDownload { get; set; } = false;
+    public int SpeedLimitKbps { get; set; } = 0;
+    public MobileThemeMode ThemeMode { get; set; } = MobileThemeMode.Dark;
+    public bool NotifyOnCompletion { get; set; } = true;
+}