feat: Add powerup inventory UI and mobile touch controls including a virtual joystick and action buttons.

scripts/ui/powerup_inventory_ui.gd

@@ -74,6 +74,35 @@ func _setup_btn(effect_id: int, btn: Button):
 		cd_lbl.text = ""
 		btn.add_child(cd_lbl)
 
+	# Add Keyboard Shortcut Label
+	if not btn.has_node("ShortcutLabel"):
+		var sc_lbl = Label.new()
+		sc_lbl.name = "ShortcutLabel"
+		sc_lbl.mouse_filter = Control.MOUSE_FILTER_IGNORE
+		sc_lbl.horizontal_alignment = HORIZONTAL_ALIGNMENT_CENTER
+		sc_lbl.vertical_alignment = VERTICAL_ALIGNMENT_BOTTOM
+		sc_lbl.set_anchors_preset(Control.PRESET_FULL_RECT)
+		# Offset slightly below or at bottom edge
+		sc_lbl.offset_bottom = 20 
+		sc_lbl.add_theme_font_size_override("font_size", 14)
+		sc_lbl.add_theme_color_override("font_outline_color", Color.BLACK)
+		sc_lbl.add_theme_constant_override("outline_size", 4)
+		
+		# Determine Label Text based on Effect ID
+		# 0: Speed -> 1
+		# 2: Wall -> 2
+		# 1: Freeze -> 3
+		# 3: Ghost -> 4
+		var key_text = ""
+		match effect_id:
+			0: key_text = "1"
+			2: key_text = "2"
+			1: key_text = "3"
+			3: key_text = "4"
+			
+		sc_lbl.text = key_text
+		btn.add_child(sc_lbl)
+
 	# Connect click
 	if not btn.pressed.is_connected(_on_btn_pressed):
 		btn.pressed.connect(_on_btn_pressed.bind(effect_id))