fix: dark overlay + pause input error

- PromotionUI: deactivate DimBG (permanent 70% black overlay) on Awake,
  show only during promotion selection
- PauseMenuController: remove Input.GetButtonDown('Pause') — button not
  defined in InputManager, use KeyCode.Escape only
- SceneTransitionManager: use Time.unscaledDeltaTime and
  WaitForSecondsRealtime so fades don't freeze when Time.timeScale=0

Assets/Game/Scripts/Mono/Core/SceneTransitionManager.cs

@@ -125,7 +125,7 @@ public class SceneTransitionManager : MonoBehaviour
         Debug.Log($"[SceneTransitionManager] Escena '{sceneName}' cargada.");
         
         // Pequeña pausa antes de fade in (para evitar flicker)
-        yield return new WaitForSeconds(0.1f);
+        yield return new WaitForSecondsRealtime(0.1f);
         
         // Fade in (negro desaparece)
         yield return FadeRoutine(1f, 0f, _fadeDuration, _fadeInCurve);
@@ -143,7 +143,7 @@ public class SceneTransitionManager : MonoBehaviour
         
         while (elapsed < duration)
         {
-            elapsed += Time.deltaTime;
+            elapsed += Time.unscaledDeltaTime;
             float normalizedTime = Mathf.Clamp01(elapsed / duration);
             float curveValue = curve.Evaluate(normalizedTime);
             float alpha = Mathf.Lerp(from, to, curveValue);

Assets/Game/Scripts/Mono/UI/PauseMenuController.cs

@@ -54,7 +54,7 @@ namespace AjedrezPurgatorio.UI
         private void Update()
         {
             // Listen for Escape key or gamepad Start button
-            if (Input.GetKeyDown(KeyCode.Escape) || Input.GetButtonDown("Pause"))
+            if (Input.GetKeyDown(KeyCode.Escape))
             {
                 if (_isPaused)
                     Hide();

Assets/Game/Scripts/Mono/UI/PromotionUI.cs

@@ -17,9 +17,18 @@ public class PromotionUI : MonoBehaviour
     
     private Piece _pawnToPromote;
     private Action<PieceType> _onPromotionSelected;
+    private GameObject _dimBG;
     
     void Awake()
     {
+        // Find DimBG sibling (always-active dark overlay blocking input)
+        Transform dimBGTransform = transform.Find("DimBG");
+        if (dimBGTransform != null)
+        {
+            _dimBG = dimBGTransform.gameObject;
+            _dimBG.SetActive(false);
+        }
+        
         if (_promotionPanel != null)
             _promotionPanel.SetActive(false);
         
@@ -48,6 +57,7 @@ public class PromotionUI : MonoBehaviour
         if (_promotionPanel != null)
         {
             _promotionPanel.SetActive(true);
+            if (_dimBG != null) _dimBG.SetActive(true);
             
             // Pausar el juego mientras el jugador elige
             Time.timeScale = 0f;
@@ -65,6 +75,7 @@ public class PromotionUI : MonoBehaviour
         // Ocultar UI
         if (_promotionPanel != null)
             _promotionPanel.SetActive(false);
+        if (_dimBG != null) _dimBG.SetActive(false);
         
         // Reanudar el juego
         Time.timeScale = 1f;