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/Materials/landMark.mat

@@ -14,7 +14,6 @@ Material:
   m_ValidKeywords:
   - _ALPHAPREMULTIPLY_ON
   - _EMISSION
-  - _SPECULAR_COLOR
   - _SURFACE_TYPE_TRANSPARENT
   m_InvalidKeywords: []
   m_LightmapFlags: 1
@@ -26,6 +25,7 @@ Material:
   disabledShaderPasses:
   - MOTIONVECTORS
   - DepthOnly
+  - SHADOWCASTER
   m_LockedProperties: 
   m_SavedProperties:
     serializedVersion: 3
@@ -55,7 +55,7 @@ Material:
         m_Scale: {x: 1, y: 1}
         m_Offset: {x: 0, y: 0}
     - _MainTex:
-        m_Texture: {fileID: 0}
+        m_Texture: {fileID: 2800000, guid: 435eb10ee7c8e0b41812b2dd39ca7e2b, type: 3}
         m_Scale: {x: 1, y: 1}
         m_Offset: {x: 0, y: 0}
     - _MetallicGlossMap:
@@ -116,10 +116,11 @@ Material:
     - _SrcBlendAlpha: 1
     - _Surface: 1
     - _UVSec: 0
+    - _XRMotionVectorsPass: 1
     - _ZWrite: 0
     m_Colors:
     - _BaseColor: {r: 0.28275868, g: 0, b: 1, a: 1}
-    - _Color: {r: 1, g: 1, b: 1, a: 1}
+    - _Color: {r: 0.28275865, g: 0, b: 1, a: 1}
     - _EmissionColor: {r: 0, g: 0, b: 0, a: 1}
     - _SpecColor: {r: 0.2, g: 0.2, b: 0.2, a: 1}
   m_BuildTextureStacks: []