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/UI/DebugFadeToggle.cs

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+using System.Collections;
+using UnityEngine;
+using UnityEngine.UI;
+
+public class DebugFadeToggle : MonoBehaviour
+{
+    public Image targetImage;
+    public float duration = 0.5f;
+
+    bool isVisible = true;
+    Coroutine running;
+    
+    void Start()
+    {
+        var btn = GetComponent<Button>();
+        if (btn != null)
+            btn.onClick.AddListener(ToggleFade);
+    }
+
+    public void ToggleFade()
+    {
+        if (targetImage == null) return;
+
+        float targetAlpha = isVisible ? 0f : 1f;
+        if (running != null) StopCoroutine(running);
+        running = StartCoroutine(FadeTo(targetAlpha));
+        isVisible = !isVisible;
+    }
+
+    IEnumerator FadeTo(float targetAlpha)
+    {
+        float start = targetImage.color.a;
+        float t = 0f;
+
+        while (t < duration)
+        {
+            t += Time.deltaTime;
+            float a = Mathf.Lerp(start, targetAlpha, Mathf.Clamp01(t / duration));
+            var c = targetImage.color;
+            c.a = a;
+            targetImage.color = c;
+            yield return null;
+        }
+
+        var final = targetImage.color;
+        final.a = targetAlpha;
+        targetImage.color = final;
+        running = null;
+    }
+}

Assets/Scripts/UI/DebugFadeToggle.cs.meta

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+fileFormatVersion: 2
+guid: e99816cb33c22f840bae5c4d5be9523f

Assets/Scripts/UI/DebugFadeToggleBridge.cs

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+using System.Collections;
+using UnityEngine;
+using UnityEngine.UI;
+
+namespace ProceduralEditor
+{
+    // Runtime helper that toggles the alpha of a target Image when the Button it's attached to is clicked.
+    public class DebugFadeToggleBridge : MonoBehaviour
+    {
+        public Image targetImage;
+        public float duration = 0.1f;
+
+        bool isVisible = true;
+        Coroutine running;
+
+        void Start()
+        {
+            var btn = GetComponent<Button>();
+            if (btn != null)
+                btn.onClick.AddListener(ToggleFade);
+        }
+
+        public void ToggleFade()
+        {
+            if (targetImage == null) return;
+
+            float targetAlpha = isVisible ? 0f : 1f;
+            if (running != null) StopCoroutine(running);
+            running = StartCoroutine(FadeTo(targetAlpha));
+            isVisible = !isVisible;
+        }
+
+        IEnumerator FadeTo(float targetAlpha)
+        {
+            float start = targetImage.color.a;
+            float t = 0f;
+
+            while (t < duration)
+            {
+                t += Time.deltaTime;
+                float a = Mathf.Lerp(start, targetAlpha, Mathf.Clamp01(t / duration));
+                var c = targetImage.color;
+                c.a = a;
+                targetImage.color = c;
+                yield return null;
+            }
+
+            var final = targetImage.color;
+            final.a = targetAlpha;
+            targetImage.color = final;
+            running = null;
+        }
+    }
+}

Assets/Scripts/UI/DebugFadeToggleBridge.cs.meta

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+fileFormatVersion: 2
+guid: 94f21b7480673b540bd619ed7bb266f9

Assets/Scripts/UI/MenuFadeIn.cs

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+using System.Collections;
+using UnityEngine;
+
+[RequireComponent(typeof(CanvasGroup))]
+public class MenuFadeIn : MonoBehaviour
+{
+    public float delay = 0.3f;
+    public float duration = 3.5f;
+
+    CanvasGroup _group;
+    Coroutine _fadeRoutine;
+
+    void Awake()
+    {
+        // Ensure a CanvasGroup exists (SetupMainMenuScene adds one, but be defensive)
+        _group = GetComponent<CanvasGroup>();
+        if (_group == null) _group = gameObject.AddComponent<CanvasGroup>();
+
+        _group.alpha = 1f;
+        _group.blocksRaycasts = true;
+        Debug.Log("[MenuFadeIn] Awake - CanvasGroup ensured, alpha=1");
+    }
+
+    void OnEnable()
+    {
+        // Reset state whenever enabled and start the fade
+        if (_group == null) _group = GetComponent<CanvasGroup>() ?? gameObject.AddComponent<CanvasGroup>();
+        _group.alpha = 1f;
+        _group.blocksRaycasts = true;
+
+        if (_fadeRoutine != null) StopCoroutine(_fadeRoutine);
+        _fadeRoutine = StartCoroutine(Fade());
+        Debug.Log("[MenuFadeIn] OnEnable - starting fade (delay=" + delay + ", duration=" + duration + ")");
+    }
+
+    void OnDisable()
+    {
+        if (_fadeRoutine != null)
+        {
+            StopCoroutine(_fadeRoutine);
+            _fadeRoutine = null;
+            Debug.Log("[MenuFadeIn] OnDisable - stopped fade coroutine");
+        }
+    }
+
+    IEnumerator Fade()
+    {
+        if (delay > 0f) yield return new WaitForSecondsRealtime(delay);
+
+        float t = 0f;
+        while (t < duration)
+        {
+            t += Time.unscaledDeltaTime;
+            _group.alpha = 1f - Mathf.Clamp01(t / duration);
+            yield return null;
+        }
+
+        _group.alpha = 0f;
+        _group.blocksRaycasts = false;
+        Debug.Log("[MenuFadeIn] Fade finished - disabling GameObject");
+        gameObject.SetActive(false);
+    }
+}

Assets/Scripts/UI/MenuFadeIn.cs.meta

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+fileFormatVersion: 2
+guid: dcac9b4ec2e8fe143ac611df7f4b548f