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/tile.mat

@@ -13,8 +13,6 @@ Material:
   m_ModifiedSerializedProperties: 0
   m_ValidKeywords:
   - _EMISSION
-  - _GLOSSINESS_FROM_BASE_ALPHA
-  - _SPECULAR_COLOR
   m_InvalidKeywords: []
   m_LightmapFlags: 1
   m_EnableInstancingVariants: 0
@@ -49,8 +47,8 @@ Material:
         m_Scale: {x: 1, y: 1}
         m_Offset: {x: 0, y: 0}
     - _MainTex:
-        m_Texture: {fileID: 0}
-        m_Scale: {x: 1, y: 1}
+        m_Texture: {fileID: 2800000, guid: 900e49f80a88714429ddb6e43b813ef6, type: 3}
+        m_Scale: {x: 5, y: 5}
         m_Offset: {x: 0, y: 0}
     - _ParallaxMap:
         m_Texture: {fileID: 0}
@@ -97,6 +95,7 @@ Material:
     - _SrcBlend: 1
     - _SrcBlendAlpha: 1
     - _Surface: 0
+    - _XRMotionVectorsPass: 1
     - _ZWrite: 1
     m_Colors:
     - _BaseColor: {r: 1, g: 1, b: 1, a: 1}