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/Dissolve.shader

@@ -1,59 +1,79 @@
-Shader "Custom/Dissolve"
+Shader "Custom/URP_Dissolve"
 {
 	Properties {
 		_Color ("Color", Color) = (1,1,1,1)
 		_MainTex ("Albedo (RGB)", 2D) = "white" {}
 		_Glossiness ("Smoothness", Range(0,1)) = 0.5
 		_Metallic ("Metallic", Range(0,1)) = 0.0
-
-		_DissolveTexture("Dissolve Texture", 2D) = "white" {} 
+		_DissolveTexture("Dissolve Texture", 2D) = "white" {}
 		_Amount("Amount", Range(0,1)) = 0
-		_DissolveColor ("Disolve Color", Color) = (1,1,1,1)
+		_DissolveColor ("Dissolve Color", Color) = (1,1,1,1)
 		_DissolveColorAlpha ("Dissolve Color Alpha", Range(0,1)) = 0.0
 	}
-	 
 	SubShader {
 		Tags { "RenderType"="Opaque" }
 		LOD 200
 		Cull Off
 
-		CGPROGRAM
-		#pragma surface surf Standard fullforwardshadows
+		Pass {
+			Name "FORWARD"
+			Tags { "LightMode" = "UniversalForward" }
 
-		#pragma target 3.0
+			HLSLPROGRAM
+			#pragma vertex vert
+			#pragma fragment frag
+			#pragma multi_compile_fog
+			#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
 
-		sampler2D _MainTex;
+			struct Attributes {
+				float4 positionOS : POSITION;
+				float2 uv         : TEXCOORD0;
+			};
 
-		struct Input {
-			float2 uv_MainTex;
-		};
+			   struct Varyings {
+				   float4 positionHCS : SV_POSITION;
+				   float2 uv          : TEXCOORD0;
+				   float fogFactor    : TEXCOORD1;
+			   };
 
-		half _Glossiness;
-		half _Metallic;
-		fixed4 _Color;
-		fixed3 _DissolveColor;
-		half _DissolveColorAlpha;
+			CBUFFER_START(UnityPerMaterial)
+				float4 _Color;
+				float _Glossiness;
+				float _Metallic;
+				float4 _DissolveColor;
+				float _DissolveColorAlpha;
+				float _Amount;
+			CBUFFER_END
 
-		//Dissolve properties
-		sampler2D _DissolveTexture;
-		half _Amount;
+			TEXTURE2D(_MainTex); SAMPLER(sampler_MainTex);
+			TEXTURE2D(_DissolveTexture); SAMPLER(sampler_DissolveTexture);
 
-		void surf (Input IN, inout SurfaceOutputStandard o) {
+			Varyings vert(Attributes IN)
+			{
+				Varyings OUT;
+				OUT.positionHCS = TransformObjectToHClip(IN.positionOS.xyz);
+				OUT.uv = IN.uv;
+			OUT.fogFactor = ComputeFogFactor(OUT.positionHCS.z / OUT.positionHCS.w);
+				return OUT;
+			}
 
-			//Dissolve function
-			half dissolve_value = tex2D(_DissolveTexture, IN.uv_MainTex).r;
-			clip(dissolve_value - _Amount);
+			float4 frag(Varyings IN) : SV_Target
+			{
+				float dissolve_value = SAMPLE_TEXTURE2D(_DissolveTexture, sampler_DissolveTexture, IN.uv).r;
+				clip(dissolve_value - _Amount);
 
-			//Basic shader function
-			fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color; 
+				float4 albedo = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, IN.uv) * _Color;
 
-			o.Albedo = c.rgb;
-			o.Metallic = _Metallic;
-			o.Smoothness = _Glossiness;
-			o.Alpha = c.a;
-			o.Emission = fixed3(_DissolveColor.r, _DissolveColor.g, _DissolveColor.b) * step( dissolve_value - _Amount, _DissolveColorAlpha); //emits white color with 0.05 border size
+				// Simple metallic/smoothness (not PBR, but for effect)
+				float3 emission = _DissolveColor.rgb * step(dissolve_value - _Amount, _DissolveColorAlpha);
+
+				float3 color = albedo.rgb + emission;
+				float alpha = albedo.a;
+			color = MixFog(color, IN.fogFactor);
+				return float4(color, alpha);
+			}
+			ENDHLSL
 		}
-		ENDCG
 	}
-	FallBack "Diffuse"
+	FallBack "Universal Forward"
 }