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/Foot Dust Particles.mat

@@ -2,19 +2,24 @@
 %TAG !u! tag:unity3d.com,2011:
 --- !u!21 &2100000
 Material:
-  serializedVersion: 6
+  serializedVersion: 8
   m_ObjectHideFlags: 0
-  m_PrefabParentObject: {fileID: 0}
-  m_PrefabInternal: {fileID: 0}
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
   m_Name: Foot Dust Particles
   m_Shader: {fileID: 203, guid: 0000000000000000f000000000000000, type: 0}
-  m_ShaderKeywords: 
+  m_Parent: {fileID: 0}
+  m_ModifiedSerializedProperties: 0
+  m_ValidKeywords: []
+  m_InvalidKeywords: []
   m_LightmapFlags: 4
   m_EnableInstancingVariants: 0
   m_DoubleSidedGI: 0
   m_CustomRenderQueue: -1
   stringTagMap: {}
   disabledShaderPasses: []
+  m_LockedProperties: 
   m_SavedProperties:
     serializedVersion: 3
     m_TexEnvs:
@@ -54,6 +59,7 @@ Material:
         m_Texture: {fileID: 0}
         m_Scale: {x: 1, y: 1}
         m_Offset: {x: 0, y: 0}
+    m_Ints: []
     m_Floats:
     - _BumpScale: 1
     - _Cutoff: 0.5
@@ -75,4 +81,6 @@ Material:
     m_Colors:
     - _Color: {r: 1, g: 1, b: 1, a: 1}
     - _EmissionColor: {r: 0, g: 0, b: 0, a: 1}
-    - _TintColor: {r: 0.74264705, g: 0.5023789, b: 0.5023789, a: 0.5}
+    - _TintColor: {r: 0.3490566, g: 0.3490566, b: 0.3490566, a: 0.5}
+  m_BuildTextureStacks: []
+  m_AllowLocking: 1