feat(ads/seo/release): v1.2.0 with live Google Ads, isolated ad profile, ads.txt, and SEO/AEO/GEO optimization

src/Paca.Core/VideoPosterExtractor.cs

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+using System;
+using System.Globalization;
+
+namespace Paca.Core;
+
+/// <summary>
+/// Image format for extracted video poster thumbnails.
+/// </summary>
+public enum PosterFormat
+{
+    Jpeg,
+    Png,
+    WebP
+}
+
+/// <summary>
+/// Specification for capturing high-quality single-frame video posters.
+/// </summary>
+public sealed record PosterExtractionSpec(
+    double SeekTimeSec,
+    int Width,
+    int Height,
+    PosterFormat Format,
+    int Quality = 85
+);
+
+/// <summary>
+/// Video poster frame extractor generating intelligent seek points and scaling pipelines.
+/// </summary>
+public static class VideoPosterExtractor
+{
+    /// <summary>
+    /// 배터리 절전 모드 활성화 시 CPU 집약적인 썸네일/포스터 프레임 추출을 일시 유예할지 판정합니다.
+    /// </summary>
+    public static bool ShouldDeferExtraction(Platform.BatterySaverPowerManager? powerManager) =>
+        powerManager?.ShouldDeferBackgroundProcessing ?? false;
+
+    /// <summary>
+    /// Computes optimal frame timestamp skipping black intro/logos while avoiding spoilers.
+    /// </summary>
+    public static double CalculateOptimalSeekTime(double totalDurationSec)
+    {
+        if (totalDurationSec <= 0)
+            return 0.0;
+
+        if (totalDurationSec < 10.0)
+            return Math.Min(1.0, totalDurationSec * 0.5);
+
+        return Math.Min(10.0, totalDurationSec * 0.1);
+    }
+
+    /// <summary>
+    /// Builds aspect-ratio preserving downscale filter.
+    /// </summary>
+    public static string BuildScalingFilter(PosterExtractionSpec spec)
+    {
+        return $"scale={spec.Width}:{spec.Height}:force_original_aspect_ratio=decrease";
+    }
+
+    /// <summary>
+    /// Builds full ffmpeg command line for single-frame thumbnail extraction.
+    /// </summary>
+    public static string BuildPosterCommandLine(
+        string inputVideoPath,
+        string outputImagePath,
+        PosterExtractionSpec spec)
+    {
+        var seekStr = spec.SeekTimeSec.ToString("F2", CultureInfo.InvariantCulture);
+        var scaleFilter = BuildScalingFilter(spec);
+
+        var encoderFlags = spec.Format switch
+        {
+            PosterFormat.WebP => $"-c:v libwebp -quality {spec.Quality}",
+            PosterFormat.Png => "-c:v png",
+            _ => "-q:v 2"
+        };
+
+        return $"-ss {seekStr} -i \"{inputVideoPath}\" -vframes 1 -vf \"{scaleFilter}\" {encoderFlags} \"{outputImagePath}\" -y";
+    }
+}