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

tests/Paca.Tests/Mobile/MobileCoreFeaturesGateTests.cs

@@ -0,0 +1,142 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Paca.Mobile.Core;
+using Xunit;
+
+namespace Paca.Tests.Mobile;
+
+/// <summary>
+/// 모바일 프로덕션 7대 핵심 기능 게이트 (Gate 87 ~ Gate 92)
+/// </summary>
+public class MobileCoreFeaturesGateTests
+{
+    [Fact]
+    public void Gate87_MobileDiscoveryEngine_UrlParsing_And_PlatformDetection_Audit()
+    {
+        // YouTube, Vimeo, Twitter, 일반 미디어 감지
+        var yt = MobileDiscoveryEngine.DetectPlatform("https://www.youtube.com/watch?v=dQw4w9WgXcQ");
+        Assert.Equal("YouTube", yt.PlatformName);
+        Assert.True(yt.IsSupported);
+
+        var vm = MobileDiscoveryEngine.DetectPlatform("https://vimeo.com/12345678");
+        Assert.Equal("Vimeo", vm.PlatformName);
+        Assert.True(vm.IsSupported);
+
+        var general = MobileDiscoveryEngine.DetectPlatform("https://example.com/video.m3u8");
+        Assert.Equal("HLS Stream", general.PlatformName);
+        Assert.True(general.IsSupported);
+
+        var unknown = MobileDiscoveryEngine.DetectPlatform("https://not-a-video.org/page.html");
+        Assert.Equal("Web Page", unknown.PlatformName);
+    }
+
+    [Fact]
+    public void Gate88_MobileQueueManager_Control_And_Retry_Audit()
+    {
+        var qm = new MobileQueueManager();
+        var item1 = qm.Enqueue("https://example.com/v1.mp4", "Video 1");
+        var item2 = qm.Enqueue("https://example.com/v2.mp4", "Video 2");
+
+        Assert.Equal(2, qm.Items.Count);
+
+        // 일시정지 & 재개
+        qm.Pause(item1.Id);
+        Assert.Equal(MobileQueueStatus.Paused, item1.Status);
+        qm.Resume(item1.Id);
+        Assert.Equal(MobileQueueStatus.Downloading, item1.Status);
+
+        // 상단 고정 (Pin)
+        qm.Pin(item2.Id);
+        Assert.True(item2.IsPinned);
+
+        // 실패 상태 설정 후 일괄 재시도 검증
+        item1.Status = MobileQueueStatus.Failed;
+        var retriedCount = qm.RetryFailedItems();
+        Assert.Equal(1, retriedCount);
+        Assert.Equal(MobileQueueStatus.Queued, item1.Status);
+
+        // 완료 항목 정리
+        item2.Status = MobileQueueStatus.Completed;
+        qm.ClearCompleted();
+        Assert.Single(qm.Items);
+    }
+
+    [Fact]
+    public void Gate89_MobileFavoritesManager_Stash_And_Tagging_Audit()
+    {
+        var fm = new MobileFavoritesManager();
+        var fav = fm.AddFavorite("https://example.com/movie.mp4", "Great Movie", "영화");
+
+        Assert.Single(fm.Favorites);
+        Assert.Equal("영화", fav.Tag);
+        Assert.False(fav.IsStashedForDownload);
+
+        // Stash(나중에 다운로드) 토글
+        fm.ToggleStash(fav.Id);
+        Assert.True(fav.IsStashedForDownload);
+
+        // 태그 검색 필터
+        var filtered = fm.GetByTag("영화");
+        Assert.Single(filtered);
+    }
+
+    [Fact]
+    public void Gate90_MobileTabSyncEngine_RemoteTabSync_Audit()
+    {
+        var sync = new MobileTabSyncEngine();
+        Assert.Empty(sync.RemoteTabs);
+
+        // PC 브라우저 탭 목록 동기화
+        var remoteTabs = new List<RemoteTabInfo>
+        {
+            new("tab-1", "GitHub Paca Repo", "https://github.com/test/paca"),
+            new("tab-2", "YouTube Video Stream", "https://youtube.com/watch?v=123")
+        };
+        sync.UpdateRemoteTabs(remoteTabs);
+
+        Assert.Equal(2, sync.RemoteTabs.Count);
+        Assert.Equal("GitHub Paca Repo", sync.RemoteTabs[0].Title);
+
+        // 모바일에서 원격 다운로드 요청 이벤트 트리거
+        string? requestedUrl = null;
+        sync.OnRemoteDownloadRequested += url => requestedUrl = url;
+        sync.RequestRemoteDownload("tab-2");
+
+        Assert.Equal("https://youtube.com/watch?v=123", requestedUrl);
+    }
+
+    [Fact]
+    public void Gate91_MobileSettingsManager_Preferences_Audit()
+    {
+        var settings = new MobileSettingsManager();
+        Assert.True(settings.AutoRetryOnReconnect);
+        Assert.False(settings.WifiOnlyDownload);
+        Assert.Equal(0, settings.SpeedLimitKbps);
+        Assert.Equal(MobileThemeMode.Dark, settings.ThemeMode);
+
+        settings.WifiOnlyDownload = true;
+        settings.SpeedLimitKbps = 2048;
+        settings.ThemeMode = MobileThemeMode.Light;
+
+        Assert.True(settings.WifiOnlyDownload);
+        Assert.Equal(2048, settings.SpeedLimitKbps);
+        Assert.Equal(MobileThemeMode.Light, settings.ThemeMode);
+    }
+
+    [Fact]
+    public void Gate92_MobileNetworkGuard_AutoResume_Audit()
+    {
+        var qm = new MobileQueueManager();
+        var guard = new MobileNetworkGuard(qm);
+
+        var item = qm.Enqueue("https://example.com/video.mp4", "Test Video");
+        item.Status = MobileQueueStatus.PausedNetwork;
+
+        // 네트워크 복구 이벤트 발생
+        guard.OnNetworkRestored(isWifi: true);
+
+        // 네트워크 단절로 멈췄던 항목이 자동으로 재개되어야 함
+        Assert.Equal(MobileQueueStatus.Downloading, item.Status);
+    }
+}