Add start game time feature to world generation; update API and UI to support custom start dates for in-world calendar

tests/TheLivingWorld.Tests/GameTimeTests.cs

@@ -58,4 +58,20 @@ public sealed class GameTimeTests
     {
         Assert.Equal(expected, GameTime.IsValidTimeScale(scale));
     }
+
+    [Fact]
+    public void ResolveStart_defaults_and_normalises()
+    {
+        Assert.Equal(GameTime.DefaultStart, GameTime.ResolveStart(null));
+        Assert.Equal(
+            new DateTime(1999, 12, 31, 23, 45, 0, DateTimeKind.Unspecified),
+            GameTime.ResolveStart(new DateTime(1999, 12, 31, 23, 45, 59, DateTimeKind.Utc)));
+    }
+
+    [Fact]
+    public void ResolveStart_rejects_out_of_range_years()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            GameTime.ResolveStart(new DateTime(10000, 1, 1)));
+    }
 }

tests/TheLivingWorld.Tests/WorldGenerationServiceTests.cs

@@ -45,6 +45,29 @@ public sealed class WorldGenerationServiceTests : IDisposable
         Assert.Equal("Taken", Assert.Single(await _store.ListAsync()).Name);
     }
 
+    [Fact]
+    public async Task StartAsync_uses_requested_start_game_time_on_the_pending_clock()
+    {
+        using var service = CreateService(maxConcurrentWorlds: 2);
+        var start = new DateTime(1995, 6, 15, 8, 30, 0, DateTimeKind.Unspecified);
+
+        var summary = await service.StartAsync(new CreateWorldRequest
+        {
+            Name = "Custom clock",
+            Latitude = 31.8966010,
+            Longitude = -100.4858591,
+            SizeKm = 5,
+            StartGameTime = start,
+        }, CancellationToken.None);
+
+        Assert.NotNull(summary.Clock);
+        Assert.Equal(start, summary.Clock.GameTime);
+
+        var stored = await _store.GetSummaryAsync(summary.Id);
+        Assert.NotNull(stored?.Clock);
+        Assert.Equal(start, stored.Clock.GameTime);
+    }
+
     private WorldGenerationService CreateService(int maxConcurrentWorlds)
     {
         // The capacity check runs before any Overpass work, so this generator is never invoked by the