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/Main.tscn

@@ -0,0 +1,20 @@
+[gd_scene load_steps=2 format=3 uid="uid://btheriapolis0m0"]
+
+[ext_resource type="Script" path="res://Main.cs" id="1_main"]
+
+[node name="Main" type="Node"]
+script = ExtResource("1_main")
+
+[node name="Label" type="Label" parent="."]
+anchors_preset = 8
+anchor_left = 0.5
+anchor_top = 0.5
+anchor_right = 0.5
+anchor_bottom = 0.5
+offset_left = -200.0
+offset_top = -16.0
+offset_right = 200.0
+offset_bottom = 16.0
+horizontal_alignment = 1
+vertical_alignment = 1
+text = "Theriapolis · Godot port · M0 · F11 toggles fullscreen"