feat(a2a): Godot 4.7 .NET project scaffold referencing Age.Engine (headless smoke)

SMOKE: Paths resolves to age-reimpl inside Godot; Age.Engine parses SC0000 in-process.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

godot/Main.tscn

@@ -0,0 +1,8 @@
+[gd_scene load_steps=2 format=3]
+
+[ext_resource type="Script" path="res://Main.cs" id="1"]
+
+[node name="Main" type="Control"]
+layout_mode = 3
+anchors_preset = 15
+script = ExtResource("1")