Add Active Buffs management and UI integration

Scripts/ActiveBuffUi.cs

@@ -0,0 +1,31 @@
+using Godot;
+using ParasiticGod.Scripts.Core.Effects;
+
+namespace ParasiticGod.Scripts;
+
+[GlobalClass]
+public partial class ActiveBuffUi : Button
+{
+    private Buff _buff;
+
+    public void SetBuff(Buff buff)
+    {
+        _buff = buff;
+        Disabled = true;
+        UpdateDisplay();
+    }
+
+    public override void _Process(double delta)
+    {
+        if (_buff != null)
+        {
+            UpdateDisplay();
+        }
+    }
+
+    private void UpdateDisplay()
+    {
+        Text = _buff.Name;
+        TooltipText = $"x{_buff.Multiplier:F1} to {_buff.Name.Split(' ')[0]}\n{_buff.Duration:F0}s remaining";
+    }
+}