M0: Scaffold Theriapolis.Godot project (hello-world)

First milestone of the Godot port. Establishes the new project structure
and verifies the toolchain is wired up end-to-end.

- Godot.NET.Sdk/4.6.2 targeting net8.0; references Theriapolis.Core
- project.godot configured for borderless fullscreen at native resolution
  (per port plan §10 resolved decisions); F11 toggles to windowed
- Main.tscn + Main.cs hello-world; nearest-neighbor texture filtering
- icon.svg placeholder (T in gild on dark)
- Added to Theriapolis.sln

Verification:
- dotnet build Theriapolis.Godot.csproj: 0 errors, 0 warnings
- dotnet build Theriapolis.sln: 0 errors (6 pre-existing warnings unrelated)
- dotnet test: 708/708 pass in 26s (unchanged from master)
- Godot 4.6.2 opens project; fullscreen + F11 toggle confirmed visually

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

Theriapolis.Godot/Theriapolis.Godot.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Godot.NET.Sdk/4.6.2">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <LangVersion>12</LangVersion>
+    <Nullable>enable</Nullable>
+    <EnableDynamicLoading>true</EnableDynamicLoading>
+    <RootNamespace>Theriapolis.GodotHost</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Theriapolis.Core\Theriapolis.Core.csproj" />
+  </ItemGroup>
+</Project>