CHALLENGE 3: A Toggleable Pause Menu
====================================================================

TASK
----
Build a Control-based pause menu that starts hidden. Bind a "pause"
action to the Escape key in the Input Map, and toggle the menu's
visibility each time it's pressed using visible = not visible.

SETUP
-----
1. Project > Project Settings > Input Map.
2. Add a "pause" action, click "+", and press the Escape key to
   bind it.
3. Add a Control node named "PauseMenu" (optionally with a Label
   child reading "Paused" so there's something visible to confirm
   against), anchored to Full Rect or Center via the Layout menu.

SOLUTION CODE (attached to PauseMenu)
--------------------------------------------
extends Control

func _ready() -> void:
    hide()

func _process(delta: float) -> void:
    if Input.is_action_just_pressed("pause"):
        visible = not visible

WHY THIS WORKS AS AN ANSWER
----------------------------
hide() in _ready() is equivalent to setting visible = false at
startup - it's the chapter's own convenience method, used here as a
slightly more readable way of expressing "start hidden" than writing
out the assignment directly, though both do the same thing.

Input.is_action_just_pressed("pause") is deliberately used instead
of is_action_pressed() (Chapter 5's distinction) - the toggle only
needs to fire once per key press, not repeatedly for as long as
Escape happens to be held down. Using is_action_pressed() here would
make the menu flicker open and closed dozens of times a second while
the key was held, since visible = not visible would flip on every
single frame it stayed true.

visible = not visible is what performs the actual toggle: each time
the condition fires, the Control's own visible property flips to the
opposite of whatever it currently is - true becomes false, false
becomes true - so pressing Escape once opens the menu, and pressing
it again closes it, with no separate "is the menu open" variable
needed since visible itself already holds that exact information.