Initial commit: Theriapolis baseline at port/godot branch point

Captures the pre-Godot-port state of the codebase. This is the rollback
anchor for the Godot port (M0 of theriapolis-rpg-implementation-plan-godot-port.md).
All Phase 0 through Phase 6.5 work is included; Phase 7 is in flight.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Theriapolis.Tests/Worldgen/BorderOrganicsTests.cs

@@ -0,0 +1,50 @@
+using Theriapolis.Core.World.Generation;
+using Theriapolis.Core.World.Generation.Stages;
+using Xunit;
+
+namespace Theriapolis.Tests.Worldgen;
+
+/// <summary>
+/// Addendum A §1: the coastline must have organic noise-based shape across a
+/// range of seeds after the BorderDistortionGen stage runs.
+///
+/// The validator counts maximal runs of consecutive border tiles in four line
+/// orientations (horizontal, vertical, both diagonals).  Any run longer than
+/// <see cref="BorderDistortionGenStage.MaxAllowedRunLength"/> tiles is a
+/// violation — this catches both axis-aligned and diagonal ruler-straight
+/// coasts, which the previous cardinal-only 3-run detector missed.
+/// </summary>
+public sealed class BorderOrganicsTests : IClassFixture<WorldCache>
+{
+    private readonly WorldCache _cache;
+
+    public BorderOrganicsTests(WorldCache cache) => _cache = cache;
+
+    private int ViolationsForSeed(ulong seed)
+    {
+        var ctx = _cache.Get(seed);
+        return BorderDistortionGenStage.CountStraightViolations(ctx);
+    }
+
+    [Fact]
+    public void Seed_CAFEBABE_HasZeroStraightViolations()
+    {
+        Assert.Equal(0, ViolationsForSeed(0xCAFEBABEUL));
+    }
+
+    [Theory]
+    [InlineData(1UL)]
+    [InlineData(42UL)]
+    [InlineData(999UL)]
+    [InlineData(0xDEAD_BEEFUL)]
+    [InlineData(0x1234_5678UL)]
+    [InlineData(0xABCD_EF01UL)]
+    [InlineData(7777777UL)]
+    [InlineData(0xFF00_FF00UL)]
+    [InlineData(314159265UL)]
+    [InlineData(271828182UL)]
+    public void TenSeeds_HaveZeroStraightViolations(ulong seed)
+    {
+        Assert.Equal(0, ViolationsForSeed(seed));
+    }
+}