feat: Add initial player scene with character models and effects, implement core lobby UI and functionality, and introduce a 3D outline shader.

assets/shaders/outline3d.gdshader

@@ -0,0 +1,21 @@
+shader_type spatial;
+render_mode cull_front, unshaded;
+
+// Controls the width of the outline
+uniform float outline_thickness : hint_range(0.0, 0.5) = 0.03;
+
+// Controls the color of the outline
+uniform vec4 outline_color : source_color = vec4(0.0, 0.0, 0.0, 1.0);
+
+void vertex() {
+	// The core of the inverted hull method:
+	// We push the vertices outward along their normal vectors.
+	// Since front faces are culled, this creates the outline border.
+	VERTEX += NORMAL * outline_thickness;
+}
+
+void fragment() {
+	// Apply the solid outline color
+	ALBEDO = outline_color.rgb;
+	ALPHA = outline_color.a;
+}