Migrate shaders to URP and add loading screen

Reworks multiple shaders and materials for URP compatibility and adds a Loading screen/scene and a few model imports. Key changes:
- Converted ProBuilder standard vertex-color shader and several particle/surface shaders to URP HLSL passes (UniversalForward, ShadowCaster, Depth, DepthNormals) preserving base texture * tint * vertex color, normal map and PBR parameters.
- Updated particle SurfaceShader_VC to a URP forward pass and simplified lighting to use URP shader library helpers.
- Updated materials (landMark, tile) to point to project textures, adjust keywords/flags (e.g. XRMotionVectorsPass, disable ShadowCaster for one), tweak tiling and base color values.
- Added a Loading screen UI (UXML, USS) and LoadingScreenController.cs plus a new Loading scene and scene metadata.
- Imported new FBX assets (T-Pose, Untitled) and updated Editor build settings / project settings to include the new Loading scene.
These changes migrate rendering code to the Universal Render Pipeline and add a basic loading UI/scene, while updating materials and project settings accordingly.

Assets/Game Kit Controller/Shaders/Projector.shader

@@ -1,10 +1,11 @@
-Shader "Custom/Projector" {
+Shader "Custom/URP_Projector"
+{
 	Properties {
 		_Color ("Tint Color", Color) = (1,1,1,1)
 		_Attenuation ("Falloff", Range(0.0, 1.0)) = 1.0
 		_ShadowTex ("Cookie", 2D) = "gray" {}
 	}
-	Subshader {
+	SubShader {
 		Tags {"Queue"="Transparent"}
 		Pass {
 			ZWrite Off
@@ -12,41 +13,51 @@
 			Blend SrcAlpha One // Additive blending
 			Offset -1, -1
 
-			CGPROGRAM
+			HLSLPROGRAM
 			#pragma vertex vert
 			#pragma fragment frag
-			#include "UnityCG.cginc"
-			
-			struct v2f {
-				float4 uvShadow : TEXCOORD0;
-				float4 pos : SV_POSITION;
+			#pragma multi_compile_fog
+			#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
+
+			struct Attributes {
+				float4 positionOS : POSITION;
 			};
-			
+
+			   struct Varyings {
+				   float4 positionHCS : SV_POSITION;
+				   float4 uvShadow    : TEXCOORD0;
+				   float fogFactor    : TEXCOORD1;
+			   };
+
+			CBUFFER_START(UnityPerMaterial)
+				float4 _Color;
+				float _Attenuation;
+			CBUFFER_END
+
+			TEXTURE2D(_ShadowTex); SAMPLER(sampler_ShadowTex);
 			float4x4 unity_Projector;
-			float4x4 unity_ProjectorClip;
-			
-			v2f vert (float4 vertex : POSITION)
+
+			Varyings vert(Attributes IN)
 			{
-				v2f o;
-				o.pos = UnityObjectToClipPos (vertex);
-				o.uvShadow = mul (unity_Projector, vertex);
-				return o;
+				Varyings OUT;
+				OUT.positionHCS = TransformObjectToHClip(IN.positionOS.xyz);
+				OUT.uvShadow = mul(unity_Projector, IN.positionOS);
+			OUT.fogFactor = ComputeFogFactor(OUT.positionHCS.z / OUT.positionHCS.w);
+				return OUT;
 			}
-			
-			sampler2D _ShadowTex;
-			fixed4 _Color;
-			float _Attenuation;
-			
-			fixed4 frag (v2f i) : SV_Target
+
+			float4 frag(Varyings IN) : SV_Target
 			{
-				// Apply alpha mask
-				fixed4 texCookie = tex2Dproj (_ShadowTex, UNITY_PROJ_COORD(i.uvShadow));
-				fixed4 outColor = _Color * texCookie.a;
-				// Attenuation
-				float depth = i.uvShadow.z; // [-1 (near), 1 (far)]
-				return outColor * clamp(1.0 - abs(depth) + _Attenuation, 0.0, 1.0);
+				float2 projUV = IN.uvShadow.xy / IN.uvShadow.w;
+				float4 texCookie = SAMPLE_TEXTURE2D(_ShadowTex, sampler_ShadowTex, projUV);
+				float4 outColor = _Color * texCookie.a;
+				float depth = IN.uvShadow.z;
+				float atten = clamp(1.0 - abs(depth) + _Attenuation, 0.0, 1.0);
+				float3 color = outColor.rgb * atten;
+			color = MixFog(color, IN.fogFactor);
+				return float4(color, outColor.a);
 			}
-			ENDCG
+			ENDHLSL
 		}
 	}
 }