Add new skills: Double Jump, Ground Pound, Brick Armor, and Brick Shield; implement skill removal signal in SkillManager (#11)

scripts/components/GroundPoundSkillComponent.cs

@@ -0,0 +1,66 @@
+using Godot;
+using Mr.BrickAdventures.scripts.interfaces;
+using Mr.BrickAdventures.scripts.Resources;
+
+namespace Mr.BrickAdventures.scripts.components;
+
+[GlobalClass]
+public partial class GroundPoundSkillComponent : Node, ISkill
+{
+    [Export] public float PoundForce { get; set; } = 1200f;
+    [Export] public PackedScene ShockwaveScene { get; set; }
+    
+    private PlayerController _player;
+    private PlayerInputHandler _input;
+    private bool _isPounding = false;
+    
+    public void Initialize(Node owner, SkillData data)
+    {
+        _player = owner as PlayerController;
+        if (_player != null)
+        {
+            _input = _player.GetNode<PlayerInputHandler>("PlayerInputHandler");
+        }
+    }
+
+    public override void _PhysicsProcess(double delta)
+    {
+        if (_player == null || _input == null)
+        {
+            return;
+        }
+        
+        // Check if we just landed from a ground pound to create the shockwave.
+        if (_isPounding && _player.IsOnFloor())
+        {
+            _isPounding = false;
+            if (ShockwaveScene != null)
+            {
+                var shockwave = ShockwaveScene.Instantiate<Node2D>();
+                _player.GetParent()?.AddChild(shockwave);
+                shockwave.GlobalPosition = _player.GlobalPosition;
+            }
+        }
+
+        // Check to initiate a ground pound. The player must be in the air.
+        if (_input.DownHeld && !_player.IsOnFloor() && !_isPounding)
+        {
+            // Apply a strong downward force, zeroing out horizontal movement.
+            _player.Velocity = new Vector2(0, PoundForce);
+            _isPounding = true;
+        }
+    }
+    
+    public void Activate() 
+    {
+        SetPhysicsProcess(true);
+    }
+    
+    public void Deactivate() 
+    {
+        SetPhysicsProcess(false);
+        _isPounding = false;
+    }
+
+    public void ApplyUpgrade(SkillUpgrade upgrade) { }
+}