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/Menus/LoadingScreen.meta

@@ -0,0 +1,8 @@
+fileFormatVersion: 2
+guid: d941a2d26357b4d45a9b8caa347d5562
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Game/Menus/LoadingScreen/LoadingScreen.uss

@@ -0,0 +1,47 @@
+/* Contenedor Principal responsivo */
+.loading-container {
+    width: 100%;
+    height: 100%;
+    flex-grow: 1;
+    background-color: #000000;
+    align-items: flex-end;
+    justify-content: flex-end;
+    position: relative;
+}
+
+/* Texto de Carga */
+.loading-text {
+    font-size: 50px;
+    color: #ffffff;
+    -unity-font-style: bold;
+    margin-right: 40px;
+    margin-bottom: 40px;
+    
+    /* 1. Hacemos la caja más ancha para que quepa "CARGANDO..." con la fuente Komika */
+    width: 350px; 
+    
+    /* 2. Anclamos el texto a la izquierda de la caja */
+    -unity-text-align: middle-left; 
+    
+    /* 3. Evitamos estrictamente que el texto salte a la siguiente línea */
+    white-space: nowrap; 
+}
+
+/* Contenedor de la Nave */
+.spaceship-icon {
+    /* 1. Quitamos position: absolute para que respete el flujo y baje a la esquina */
+    position: relative;
+    
+    /* 2. Tamaño ajustado */
+    width: 250px;
+    height: 250px;
+    
+    /* 3. Márgenes para alinearla con el texto (mismo margin-left que el texto) */
+    margin-left: 40px;
+    
+    /* 4. Un pequeño margen abajo para que no pegue con las letras */
+    margin-bottom: -20px; 
+    
+    /* Ajuste de imagen */
+    -unity-background-scale-mode: scale-to-fit;
+}

Assets/Game/Menus/LoadingScreen/LoadingScreen.uss.meta

@@ -0,0 +1,12 @@
+fileFormatVersion: 2
+guid: 2338a47a6d4bdf04fb16da5ab852dee3
+ScriptedImporter:
+  internalIDToNameTable: []
+  externalObjects: {}
+  serializedVersion: 2
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
+  script: {fileID: 12385, guid: 0000000000000000e000000000000000, type: 0}
+  disableValidation: 0
+  unsupportedSelectorAction: 0

Assets/Game/Menus/LoadingScreen/LoadingScreen.uxml

@@ -0,0 +1,7 @@
+<ui:UXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ui="UnityEngine.UIElements" xmlns:uie="UnityEditor.UIElements" editor-extension-mode="False">
+    <Style src="project://database/Assets/Game/Menus/LoadingScreen/LoadingScreen.uss?fileID=7433441132597879392&amp;guid=2338a47a6d4bdf04fb16da5ab852dee3&amp;type=3#LoadingScreen"/>
+    <ui:VisualElement name="Container" class="loading-container" style="aspect-ratio: 1.777778;">
+        <ui:VisualElement name="Spaceship" class="spaceship-icon"/>
+        <ui:Label text="Cargando" name="LoadingText" class="loading-text" style="-unity-font-definition: url(&quot;project://database/Assets/Game/Menus/Fonts/KOMIKAX_.ttf?fileID=12800000&amp;guid=afbd8b3e208400c4ebf47631612ef61f&amp;type=3#KOMIKAX_&quot;);"/>
+    </ui:VisualElement>
+</ui:UXML>

Assets/Game/Menus/LoadingScreen/LoadingScreen.uxml.meta

@@ -0,0 +1,10 @@
+fileFormatVersion: 2
+guid: 574e334a49fbd6945b59354aed996919
+ScriptedImporter:
+  internalIDToNameTable: []
+  externalObjects: {}
+  serializedVersion: 2
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
+  script: {fileID: 13804, guid: 0000000000000000e000000000000000, type: 0}

Assets/Game/Menus/LoadingScreen/LoadingScreenController.cs

@@ -0,0 +1,80 @@
+using UnityEngine;
+using UnityEngine.UIElements;
+using UnityEngine.SceneManagement;
+using System.Collections;
+
+public class LoadingScreenController : MonoBehaviour
+{
+    private UIDocument _doc;
+    private Label _loadingText;
+    private VisualElement _spaceship;
+    
+    private int _dotCount = 0;
+    private float _time = 0f;
+
+    [Header("Configuración de Carga")]
+    public string sceneToLoad = "SampleScene";
+
+    private void Awake()
+    {
+        _doc = GetComponent<UIDocument>();
+        var root = _doc.rootVisualElement;
+
+        _loadingText = root.Q<Label>("LoadingText");
+        _spaceship = root.Q<VisualElement>("Spaceship");
+
+        // 1. Animación del texto: Se ejecuta cada 400 milisegundos
+        root.schedule.Execute(UpdateLoadingText).Every(400);
+
+        // 2. Animación loca de la nave: Se ejecuta cada 20 milisegundos para fluidez
+        root.schedule.Execute(AnimateSpaceship).Every(20);
+
+        // 3. Iniciar la carga de la escena en segundo plano
+        StartCoroutine(LoadSceneAsync());
+    }
+
+    private void UpdateLoadingText()
+    {
+        // Alterna entre 0 y 3 puntos
+        _dotCount = (_dotCount + 1) % 4;
+        _loadingText.text = "Cargando" + new string('.', _dotCount);
+    }
+
+    private void AnimateSpaceship()
+    {
+        if (_spaceship == null) return;
+
+        _time += 0.1f;
+        
+        // Efecto "Rabbid": vibración y rotación errática usando Seno y Coseno
+        float offsetX = Mathf.Sin(_time * 12f) * 8f;
+        float offsetY = Mathf.Cos(_time * 15f) * 6f;
+        float rotation = Mathf.Sin(_time * 20f) * 3f;
+
+        _spaceship.style.translate = new Translate(offsetX, offsetY, 0);
+        _spaceship.style.rotate = new Rotate(new Angle(rotation, AngleUnit.Degree));
+    }
+
+    private IEnumerator LoadSceneAsync()
+    {
+        // Pequeña pausa opcional para que la pantalla no parpadee si la escena carga muy rápido
+        yield return new WaitForSeconds(0.5f);
+
+        AsyncOperation asyncLoad = SceneManager.LoadSceneAsync(sceneToLoad);
+
+        // La escena no cambia automáticamente hasta que nosotros lo indiquemos
+        asyncLoad.allowSceneActivation = false;
+
+        // Espera hasta que Unity haya cargado el 90% (el 10% restante es la activación)
+        while (asyncLoad.progress < 0.9f)
+        {
+            yield return null;
+        }
+
+        // Pequeña pausa para que la animación sea visible aunque la escena cargue muy rápido
+        yield return new WaitForSeconds(0.8f);
+
+        // Ahora sí, activa la escena
+        asyncLoad.allowSceneActivation = true;
+    }
+}

Assets/Game/Menus/LoadingScreen/LoadingScreenController.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 62ff0d03d5ac484428d8223d73a8b8b2

Assets/Game/Menus/MainMenu/MainMenu.tss

@@ -1 +1,2 @@
-@import url("project://database/Assets/UI Toolkit/UnityThemes/UnityDefaultRuntimeTheme.tss");
+
+@import url("MainMenu.uss");

Assets/Game/Menus/MainMenu/MainMenuController.cs

@@ -47,8 +47,8 @@ public class MainMenuController : MonoBehaviour
     private void OnPlayClicked()
     {
         PlayClickSound();
-        Debug.Log("¡BWAAAH! Iniciando juego...");
-        // SceneManager.LoadScene("GameScene");
+        Debug.Log("Cargando SampleScene...");
+        SceneManager.LoadScene("Loading");
     }
 
     private void OnSettingsClicked()