feat(progression): Profile aggregate (slice 4)

best times only improve; achievement unlock announces on the transition
only, so popup/Steam subscribers cannot double-fire; statistics are
increase-only (IncrementStat took any int).

RelockAchievement is console-only and documented as not reaching Steam -
a Steam achievement cannot be un-earned, so the disagreement is
permanent and deliberate.

refactor: extract EventLog, composed by both aggregates now that the
duplication actually exists. 34 tests.

progression.tests/ProfileTests.cs

@@ -0,0 +1,74 @@
+namespace Mr.BrickAdventures.Progression.Tests;
+
+public class ProfileTests
+{
+    private static readonly LevelId Level = LevelId.Of("village_1");
+
+    [Fact]
+    public void A_slower_run_does_not_replace_a_better_time()
+    {
+        var profile = Profile.Empty();
+
+        Assert.True(profile.RecordTime(Level, LevelTime.Of(42.5)));
+        Assert.False(profile.RecordTime(Level, LevelTime.Of(51.0)));
+
+        Assert.Equal(LevelTime.Of(42.5), profile.BestTimeFor(Level));
+    }
+
+    [Fact]
+    public void Unlocking_the_same_achievement_twice_announces_it_once()
+    {
+        // AchievementManager shows a popup and pushes to Steam on every unlock call, guarded only by
+        // a Contains check on a list it reached into. Announcing only on the transition means
+        // subscribers cannot double-fire regardless of how often they are told.
+        var rescueTen = AchievementId.Of("rescue_ten_kids");
+        var profile = Profile.Empty();
+
+        profile.UnlockAchievement(rescueTen);
+        profile.UnlockAchievement(rescueTen);
+
+        Assert.True(profile.HasAchievement(rescueTen));
+        Assert.Single(profile.DrainEvents().OfType<AchievementUnlocked>());
+    }
+
+    [Fact]
+    public void Statistics_accumulate_and_an_unrecorded_one_reads_as_zero()
+    {
+        var profile = Profile.Empty();
+
+        profile.Record(StatName.CoinsCollected, 5);
+        profile.Record(StatName.CoinsCollected, 3);
+
+        Assert.Equal(8, profile.ReadStat(StatName.CoinsCollected));
+        Assert.Equal(0, profile.ReadStat(StatName.Deaths));
+    }
+
+    [Fact]
+    public void A_statistic_cannot_be_decremented()
+    {
+        // IncrementStat currently takes any int. A lifetime counter that can go down is not a
+        // lifetime counter, and nothing in the game has a reason to reduce one.
+        var profile = Profile.Empty();
+
+        Assert.Throws<ArgumentOutOfRangeException>(() => profile.Record(StatName.Deaths, -1));
+        Assert.Throws<ArgumentOutOfRangeException>(() => profile.Record(StatName.Deaths, 0));
+    }
+
+    [Fact]
+    public void Relocking_an_achievement_removes_it_and_lets_it_announce_again()
+    {
+        // Console-only. Note the asymmetry: unlocking is mirrored to Steam by a subscriber, but
+        // relocking cannot be, because a Steam achievement cannot be un-earned.
+        var rescueTen = AchievementId.Of("rescue_ten_kids");
+        var profile = Profile.Empty();
+        profile.UnlockAchievement(rescueTen);
+        profile.DrainEvents();
+
+        profile.RelockAchievement(rescueTen);
+
+        Assert.False(profile.HasAchievement(rescueTen));
+
+        profile.UnlockAchievement(rescueTen);
+        Assert.Single(profile.DrainEvents().OfType<AchievementUnlocked>());
+    }
+}