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/Settings/PC_RPAsset.asset

@@ -12,8 +12,8 @@ MonoBehaviour:
   m_Script: {fileID: 11500000, guid: bf2edee5c58d82540a51f03df9d42094, type: 3}
   m_Name: PC_RPAsset
   m_EditorClassIdentifier: 
-  k_AssetVersion: 12
-  k_AssetPreviousVersion: 12
+  k_AssetVersion: 13
+  k_AssetPreviousVersion: 13
   m_RendererType: 1
   m_RendererData: {fileID: 0}
   m_RendererDataList:
@@ -25,7 +25,7 @@ MonoBehaviour:
   m_SupportsTerrainHoles: 1
   m_SupportsHDR: 1
   m_HDRColorBufferPrecision: 0
-  m_MSAA: 1
+  m_MSAA: 8
   m_RenderScale: 1
   m_UpscalingFilter: 0
   m_FsrOverrideSharpness: 0
@@ -74,7 +74,6 @@ MonoBehaviour:
   m_MixedLightingSupported: 1
   m_SupportsLightCookies: 1
   m_SupportsLightLayers: 1
-  m_DebugLevel: 0
   m_StoreActionsOptimization: 0
   m_UseAdaptivePerformance: 1
   m_ColorGradingMode: 0
@@ -128,12 +127,15 @@ MonoBehaviour:
   m_PrefilterSoftShadowsQualityHigh: 1
   m_PrefilterSoftShadows: 0
   m_PrefilterScreenCoord: 1
+  m_PrefilterScreenSpaceIrradiance: 0
   m_PrefilterNativeRenderPass: 1
   m_PrefilterUseLegacyLightmaps: 0
   m_PrefilterBicubicLightmapSampling: 1
+  m_PrefilterReflectionProbeRotation: 0
   m_PrefilterReflectionProbeBlending: 0
   m_PrefilterReflectionProbeBoxProjection: 0
   m_PrefilterReflectionProbeAtlas: 0
+  m_PrefilterPointSamplingUpsampling: 0
   m_ShaderVariantLogLevel: 0
   m_ShadowCascades: 0
   m_Textures: