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

tests/Paca.Tests/Core/DownloadTokenBucketRateLimiterGateTests.cs

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+using System;
+using Paca.Mobile.Core;
+using Xunit;
+
+namespace Paca.Tests.Core;
+
+public class DownloadTokenBucketRateLimiterGateTests
+{
+    [Fact]
+    public void Gate453_DownloadTokenBucketRateLimiter_AllowsImmediateConsumption_WhenBucketFull()
+    {
+        var now = DateTime.UtcNow;
+        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 2_000_000, initialTime: now);
+
+        var decision = limiter.Request(500_000, now);
+
+        Assert.True(decision.IsAllowedImmediately);
+        Assert.Equal(TimeSpan.Zero, decision.DelayRequired);
+        Assert.Equal(1_500_000, limiter.AvailableTokens, 1);
+    }
+
+    [Fact]
+    public void Gate454_DownloadTokenBucketRateLimiter_CalculatesRequiredDelay_WhenTokensExhausted()
+    {
+        var now = DateTime.UtcNow;
+        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 1_000_000, initialTime: now);
+
+        // Exhaust all tokens
+        limiter.Request(1_000_000, now);
+
+        // Request another 500KB immediately (needs 500ms refill)
+        var decision = limiter.Request(500_000, now);
+
+        Assert.False(decision.IsAllowedImmediately);
+        Assert.Equal(TimeSpan.FromMilliseconds(500), decision.DelayRequired);
+    }
+
+    [Fact]
+    public void Gate455_DownloadTokenBucketRateLimiter_RefillsTokensOverTime_UpToCapacity()
+    {
+        var now = DateTime.UtcNow;
+        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 2_000_000, initialTime: now);
+
+        // Consume everything
+        limiter.Request(2_000_000, now);
+        Assert.Equal(0, limiter.AvailableTokens, 1);
+
+        // Advance time by 3 seconds (3MB generated, capped at 2MB burst)
+        var future = now.AddSeconds(3);
+        var decision = limiter.Request(1, future);
+
+        Assert.True(decision.IsAllowedImmediately);
+        Assert.Equal(2_000_000 - 1, limiter.AvailableTokens, 1);
+    }
+
+    [Fact]
+    public void Gate456_DownloadTokenBucketRateLimiter_DynamicRateAdjustment_PreservesTokens()
+    {
+        var now = DateTime.UtcNow;
+        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 2_000_000, initialTime: now);
+
+        limiter.Request(1_000_000, now);
+        Assert.Equal(1_000_000, limiter.AvailableTokens, 1);
+
+        // Adjust rate to 5 MB/s
+        limiter.SetRate(5_000_000, now);
+        Assert.Equal(1_000_000, limiter.AvailableTokens, 1);
+        Assert.Equal(5_000_000, limiter.RateBytesPerSec);
+    }
+}