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/MobileAdvancedConnectivityGateTests.cs

@@ -0,0 +1,107 @@
+using System;
+using System.Collections.Generic;
+using Paca.Mobile.Core;
+using Xunit;
+
+namespace Paca.Tests.Mobile;
+
+/// <summary>
+/// 로컬 기기 디스커버리, 원격 클립보드, 절전/데이터 가드 및 복원성 게이트 (Gate 109 ~ Gate 114)
+/// </summary>
+public class MobileAdvancedConnectivityGateTests
+{
+    [Fact]
+    public void Gate109_PacaHostBeacon_Discovery_Audit()
+    {
+        var beacon = new PacaHostBeacon();
+        var beaconPayload = "PACA_BEACON|DESKTOP-PACA|192.168.1.100:52100|token123";
+        var host = beacon.ParseBeacon(beaconPayload);
+
+        Assert.NotNull(host);
+        Assert.Equal("DESKTOP-PACA", host.HostName);
+        Assert.Equal("192.168.1.100:52100", host.Endpoint);
+        Assert.Equal("token123", host.AuthToken);
+    }
+
+    [Fact]
+    public void Gate110_CrossDeviceClipboardSync_Audit()
+    {
+        var clipSync = new CrossDeviceClipboardSync();
+        string? receivedUrl = null;
+        clipSync.OnMediaUrlReceived += url => receivedUrl = url;
+
+        // PC로부터 수신된 클립보드 패킷 처리
+        clipSync.ProcessIncomingPayload("https://twitter.com/test/status/123456");
+        Assert.Equal("https://twitter.com/test/status/123456", receivedUrl);
+
+        // 비미디어 텍스트는 필터링되어 무시되어야 함
+        receivedUrl = null;
+        clipSync.ProcessIncomingPayload("Hello this is not a media url");
+        Assert.Null(receivedUrl);
+    }
+
+    [Fact]
+    public void Gate111_MobilePowerSaverPolicy_Audit()
+    {
+        var policy = new MobilePowerSaverPolicy();
+        // 기본 6 세그먼트
+        Assert.Equal(6, policy.GetRecommendedSegments(batteryLevelPercent: 80, isCharging: false));
+
+        // 배터리 15% 이하 저전력 모드 -> 2개로 제한
+        Assert.Equal(2, policy.GetRecommendedSegments(batteryLevelPercent: 12, isCharging: false));
+
+        // 충전 중일 때는 100% 터보 허용
+        Assert.Equal(16, policy.GetRecommendedSegments(batteryLevelPercent: 12, isCharging: true));
+    }
+
+    [Fact]
+    public void Gate112_MobileDataSaverGuard_Audit()
+    {
+        var dataGuard = new MobileDataSaverGuard();
+        // 100MB 기본 임계값
+        Assert.Equal(100_000_000L, dataGuard.CellularWarningThresholdBytes);
+
+        // Wi-Fi 상태에서는 대용량도 즉시 허용
+        Assert.True(dataGuard.CanDownload(fileSizeBytes: 500_000_000, isWifi: true));
+
+        // 셀룰러 상태에서 500MB는 경고 플래그
+        Assert.False(dataGuard.CanDownload(fileSizeBytes: 500_000_000, isWifi: false));
+
+        // 셀룰러 상태에서 50MB는 허용
+        Assert.True(dataGuard.CanDownload(fileSizeBytes: 50_000_000, isWifi: false));
+    }
+
+    [Fact]
+    public void Gate113_MobileThumbnailCacheManager_Audit()
+    {
+        var cache = new MobileThumbnailCacheManager();
+        Assert.Null(cache.Get("test-key"));
+
+        cache.Put("test-key", new byte[] { 0xFF, 0xD8, 0xFF });
+        var cached = cache.Get("test-key");
+        Assert.NotNull(cached);
+        Assert.Equal(3, cached.Length);
+
+        // 캐시 삭제
+        cache.Evict("test-key");
+        Assert.Null(cache.Get("test-key"));
+    }
+
+    [Fact]
+    public void Gate114_NetworkFlapping_Stress_Resilience_Audit()
+    {
+        var qm = new MobileQueueManager();
+        var guard = new MobileNetworkGuard(qm);
+        var item = qm.Enqueue("https://example.com/live.m3u8", "Live Stream");
+        item.Status = MobileQueueStatus.Downloading;
+
+        // 10회 연속 단절 및 재연결 플래핑 스트레스
+        for (int i = 0; i < 10; i++)
+        {
+            guard.OnNetworkLost();
+            Assert.Equal(MobileQueueStatus.PausedNetwork, item.Status);
+            guard.OnNetworkRestored(isWifi: (i % 2 == 0));
+            Assert.Equal(MobileQueueStatus.Downloading, item.Status);
+        }
+    }
+}