Added gameplay_input manager.

Refactored menus, player, and escape_capsule to utilize new system.
Actions defined in Godot project file with default bindings.
Player/Vehicles now react to actions and GameplayInput states instead of polling Input directly.
They respond to commands via `_handle_gameplay_command` and should not implement _unhandled_input directly.
Kept some debugging input handling code in `player.gd` for things like F3/F5/F4/PageUp/PageDown.
We may want to move much of this out of `player.gd` into something that handles the gamestate more generally.

Scenes/Scripts/vendor_menu.gd

@@ -71,10 +71,14 @@ func _ready() -> void:
 	
 	visible = false
 
+## Claims menu input and gives controllers a predictable initial focus.
 func open_menu(player_ref: Node) -> void:
 	player = player_ref
 	visible = true
+	GameplayInput.set_menu_open(self, true)
+	Input.mouse_mode = Input.MOUSE_MODE_VISIBLE
 	_update_button_states()
+	close_button.grab_focus()
 	print("Vendor menu opened")
 
 func _update_button_states() -> void:
@@ -112,6 +116,15 @@ func _buy(item_name: String, price: int) -> void:
 	else:
 		print("Not enough credits")
 
+## Cancels the vendor without allowing the same event to reach gameplay.
+func _unhandled_input(event: InputEvent) -> void:
+	if visible and event.is_action_pressed("ui_cancel"):
+		_on_close_pressed()
+		get_viewport().set_input_as_handled()
+
+
+## Releases menu ownership; the adapter clears queued and held commands.
 func _on_close_pressed() -> void:
 	visible = false
+	GameplayInput.set_menu_open(self, false)
 	Input.mouse_mode = Input.MOUSE_MODE_CAPTURED