add-mechanic

# Add Mechanic Add game mechanics using correct GDScript 4.x syntax. Prevents common LLM mistakes with outdated GDScript 3.x patterns. ## GDScript 4.x Syntax Rules These changed from Godot 3 to 4. LLMs frequently generate the OLD syntax: | Correct (GDScript 4.x) | Wrong (GDScript 3.x -- will error) | |---|---| | `@export var speed: float = 200.0` | `export var speed = 200.0` | | `@onready var sprite = $Sprite2D` | `onready var sprite = $Sprite2D` | | `signal health_changed(new_hp: int)` | `signal health_changed` (no typed params) | | `func _ready() -> void:` | `func _ready():` (return type optional but preferred) | | `velocity = Vector2(...)` then `move_and_slide()` | `move_and_slide(velocity, Vector2.UP)` (args removed in 4.x) | | `super()` | `.method()` for parent calls | | `await get_tree().create_timer(1.0).timeout` | `yield(get_tree().create_timer(1.0), "timeout")` | | `%UniqueNode` | `get_node("path/to/node")` when unique name is set | ## Movement Patterns ### Platformer Movement ```gdscript extends CharacterBody2D @export var speed: float = 300.0 @export var jump_velocity: float = -400.0 @export var gravity: float = 980.0 func _physics_process(delta: float) -> void: # Gravity if not is_on_floor(): velocity.y += gravity * delta # Jump if Input.is_action_just_pressed("jump") and is_on_floor(): velocity.y = jump_velocity # Horizontal movement var direction := Input.get_axis("move_left", "move_right") velocity.x = direc...