Add main menu scene with Rive UI, procedural background, and scene transitions

- Add Menu scene with Rive-driven login and navigation UI
  (RiveLoginController, RiveNavigationController) for entering a
  username and starting/navigating the client via Rive triggers
- Add SceneTransitionController to fade out and load the Landscape
  gameplay scene when Play is selected
- Add procedural low-poly triangle field background and animated wave
  panel (LowPolyTriangleField, TriangleWavePanel) with matching
  editor menus and materials
- Add MenuLightAnimator for animated menu lighting and UI fade helpers
  (MenuFadeIn, DebugFadeToggle/Bridge)
- Rename SampleScene to Landscape and wire ChatNetworkManager to hide
  the new Rive login canvas once gameplay starts
- Bump Input System action codegen version and add Rive package
  references/project settings updates to support the new UI

Assets/Scripts/Chat/ChatNetworkManager.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 public class ChatNetworkManager : NetworkManager
 {
     [SerializeField] private GameObject chatUIPrefab;
+    [SerializeField] private GameObject riveLoginCanvas;
 
     // Server-side authoritative store of chat messages
     private readonly List<string> chatMessages = new();
@@ -61,6 +62,11 @@ public class ChatNetworkManager : NetworkManager
             return;
         }
 
+        if (riveLoginCanvas == null)
+        {
+            Debug.LogError("ChatNetworkManager: Rive Login Canvas is not assigned in the inspector!");
+        }
+
         // Check if ChatUI already exists to avoid duplicates
         ChatUI existingChatUI = FindFirstObjectByType<ChatUI>();
         if (existingChatUI == null)
@@ -80,6 +86,9 @@ public class ChatNetworkManager : NetworkManager
         {
             LoginUI.instance.gameObject.SetActive(false);
         }
+
+        if (riveLoginCanvas != null)
+            riveLoginCanvas.SetActive(false);
     }
 
     [Server]