MonoGame UI focus system and gamepad navigation — FocusManager singleton, keyboard input routing to the focused element, D-Pad neighbor-ID navigation, tab order, and grid auto-assignment. Use this skill whenever the user asks about keyboard navigation in menus, gamepad controller UI navigation, focus management, tab order, D-Pad menu navigation, "how do I navigate my menu with a controller", neighbor IDs, or any question about which UI element receives keyboard/gamepad input in MonoGame.
