refactor(gui): move the F-key geometry into function_row/key_points.rs

function_row.rs held the Keys tab view, its pane and callout elements, and two hundred lines resolving where each function key sits on the keyboard render: the KeyPoint marker, the metadata readers for percent- and pixel-marker depots, the synthesized Esc, the even-spacing fallback and the six constants only they read. That is key_points.rs now; the view keeps calling key_points(), and the tests reach the two spacing constants and key_x_fractions through the module's imports.

Pure move: no line inside the moved items changed beyond pub(super) on what the view and its tests reach.