feat(DevRoom): add HUD prefab and DevRoomHUD script for controls display

Assets/Code/Scripts/DevRoom/DevRoomHUD.cs

@@ -0,0 +1,90 @@
+using UnityEngine;
+
+/// <summary>
+/// Displays a controls legend in the top-left corner of the screen.
+/// Attach to any active GameObject in the DevRoom scene.
+/// </summary>
+public class DevRoomHUD : MonoBehaviour
+{
+    [Header("Layout")]
+    [SerializeField] private float paddingX = 16f;
+    [SerializeField] private float paddingY = 16f;
+    [SerializeField] private float lineHeight = 22f;
+    [SerializeField] private int fontSize = 14;
+
+    [Header("Style")]
+    [SerializeField] private Color backgroundColor = new Color(0f, 0f, 0f, 0.55f);
+    [SerializeField] private Color keyColor = new Color(1f, 0.85f, 0.2f);
+    [SerializeField] private Color labelColor = Color.white;
+
+    private static readonly (string key, string action)[] k_Controls =
+    {
+        ("WASD / Arrows", "Move"),
+        ("Mouse",         "Look"),
+        ("Space",         "Jump"),
+        ("Left Shift",    "Sprint"),
+        ("C",             "Crouch"),
+        ("LMB",           "Throw head"),
+        ("E (hold)",      "Retrieve head"),
+        ("1 / 2",         "Previous / Next"),
+    };
+
+    private GUIStyle m_keyStyle;
+    private GUIStyle m_labelStyle;
+    private GUIStyle m_boxStyle;
+    private Texture2D m_bgTexture;
+
+    private void OnGUI()
+    {
+        EnsureStyles();
+
+        float keyColWidth   = 110f;
+        float labelColWidth = 130f;
+        float totalWidth    = paddingX * 2 + keyColWidth + 8f + labelColWidth;
+        float totalHeight   = paddingY * 2 + k_Controls.Length * lineHeight;
+
+        Rect bgRect = new Rect(8f, 8f, totalWidth, totalHeight);
+        GUI.DrawTexture(bgRect, m_bgTexture);
+
+        float x = bgRect.x + paddingX;
+        float y = bgRect.y + paddingY;
+
+        for (int i = 0; i < k_Controls.Length; i++)
+        {
+            float rowY = y + i * lineHeight;
+
+            GUI.Label(new Rect(x, rowY, keyColWidth, lineHeight), k_Controls[i].key, m_keyStyle);
+            GUI.Label(new Rect(x + keyColWidth + 8f, rowY, labelColWidth, lineHeight), k_Controls[i].action, m_labelStyle);
+        }
+    }
+
+    private void EnsureStyles()
+    {
+        if (m_keyStyle != null)
+            return;
+
+        m_bgTexture = new Texture2D(1, 1);
+        m_bgTexture.SetPixel(0, 0, backgroundColor);
+        m_bgTexture.Apply();
+
+        m_keyStyle = new GUIStyle(GUI.skin.label)
+        {
+            fontSize  = fontSize,
+            fontStyle = FontStyle.Bold,
+        };
+        m_keyStyle.normal.textColor = keyColor;
+
+        m_labelStyle = new GUIStyle(GUI.skin.label)
+        {
+            fontSize  = fontSize,
+            fontStyle = FontStyle.Normal,
+        };
+        m_labelStyle.normal.textColor = labelColor;
+    }
+
+    private void OnDestroy()
+    {
+        if (m_bgTexture != null)
+            Destroy(m_bgTexture);
+    }
+}