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

UserSettings/EditorUserSettings.asset

@@ -5,6 +5,15 @@ EditorUserSettings:
   m_ObjectHideFlags: 0
   serializedVersion: 4
   m_ConfigSettings:
+    GraphicsSettingsInspector_UserSettings:
+      value: 18134705175a055722080a3115371d4a0d55006876786860616b0471b8b26368acb72ba5a52a362c3c0ee63201181433fe3e101bf3250b06144ca74c33ea191f058831cb58d5
+      flags: 0
+    QuickInstaller_com.unity.purchasing_installRecorded:
+      value: 2550581500
+      flags: 0
+    QuickInstaller_com.unity.services.levelplay_installRecorded:
+      value: 2550581500
+      flags: 0
     RecentlyUsedSceneGuid-0:
       value: 540355535d545b5e5e0f5c7212770843414e4d7b7c7c27607e7e4430b7e2646a
       flags: 0
@@ -24,10 +33,13 @@ EditorUserSettings:
       value: 0505515e01010d5e595a547615770b1214164e7c7a2e74347c2f4b65e1b7673d
       flags: 0
     RecentlyUsedSceneGuid-6:
-      value: 5a08575f5207595a0f5d59741173094444164f7d7d2a23317c7a4465bbe1646d
+      value: 0750525254025b0e095c0a2044740944474e1e2f7d2d7f657b2b4b30e0e3636f
       flags: 0
     RecentlyUsedSceneGuid-7:
-      value: 0750525254025b0e095c0a2044740944474e1e2f7d2d7f657b2b4b30e0e3636f
+      value: 5a08575f5207595a0f5d59741173094444164f7d7d2a23317c7a4465bbe1646d
+      flags: 0
+    RecentlyUsedSceneGuid-8:
+      value: 0505025f54535f035e0a0d7442710b4413151b7e787b25662e714c35e0b9323b
       flags: 0
     vcSharedLogLevel:
       value: 0d5e400f0650