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/Persistence/V7ToV8MigrationTests.cs

@@ -0,0 +1,71 @@
+using Theriapolis.Core;
+using Theriapolis.Core.Persistence;
+using Theriapolis.Core.Persistence.SaveMigrations;
+using Xunit;
+
+namespace Theriapolis.Tests.Persistence;
+
+/// <summary>
+/// Phase 7 M0 — additive V7→V8 migration. Phase-6.5 saves continue to
+/// load post-Phase-7; the new <see cref="SaveBody"/> sections (anchors,
+/// building deltas, dungeon state) default-initialise to empty, which
+/// correctly represents "no anchors persisted, no buildings modified,
+/// no dungeons visited" — the truth for any pre-Phase-7 save.
+/// </summary>
+public sealed class V7ToV8MigrationTests
+{
+    [Fact]
+    public void V7Header_IsAcceptedByMigration()
+    {
+        var header = new SaveHeader { Version = 7 };
+        Assert.True(SaveCodec.IsCompatible(header),
+            "v7 must remain readable post-Phase-7 (MIN_VERSION = 5; v7 is one bump back).");
+
+        var body = new SaveBody();
+        bool ok = Migrations.MigrateUp(header, body);
+        Assert.True(ok);
+        Assert.Equal(C.SAVE_SCHEMA_VERSION, header.Version);
+    }
+
+    [Fact]
+    public void V6Header_ChainsThroughV7ToV8()
+    {
+        // v6 → v7 → v8 chain: a Phase-6 save should still load with two
+        // additive migrations applied in order.
+        var header = new SaveHeader { Version = 6 };
+        Assert.True(SaveCodec.IsCompatible(header));
+
+        var body = new SaveBody();
+        bool ok = Migrations.MigrateUp(header, body);
+        Assert.True(ok);
+        Assert.Equal(C.SAVE_SCHEMA_VERSION, header.Version);
+    }
+
+    [Fact]
+    public void V7SaveBody_AfterMigration_PreservesPhase65Fields()
+    {
+        var header = new SaveHeader { Version = 7 };
+        var body = new SaveBody
+        {
+            Player = new() { Name = "Wanderer", PositionX = 10, PositionY = 10 },
+            PlayerCharacter = new()
+            {
+                CladeId = "canidae", SpeciesId = "wolf",
+                ClassId = "fangsworn", BackgroundId = "pack_raised",
+                STR = 15, DEX = 12, CON = 13, INT = 10, WIS = 13, CHA = 8,
+                Level = 3, Xp = 950, MaxHp = 28, CurrentHp = 28,
+                SubclassId = "pack_forged",
+                LearnedFeatureIds = new[] { "packmates_howl" },
+            },
+        };
+
+        bool ok = Migrations.MigrateUp(header, body);
+        Assert.True(ok);
+        Assert.Equal(C.SAVE_SCHEMA_VERSION, header.Version);
+
+        // Phase 6.5 fields untouched.
+        Assert.Equal(3, body.PlayerCharacter!.Level);
+        Assert.Equal("pack_forged", body.PlayerCharacter.SubclassId);
+        Assert.Contains("packmates_howl", body.PlayerCharacter.LearnedFeatureIds);
+    }
+}