Move MouseEvent and MouseFormat out of Terminal.zig and MouseShape out of mouse_shape.zig into a new mouse.zig file. The types are named without the Mouse prefix inside the module (Event, Format, Shape) and re-exported with the prefix from terminal/main.zig for external use. Update all call sites (mouse_encode.zig, surface_mouse.zig, stream.zig) to import through terminal/main.zig or directly from mouse.zig. Remove the now-unused mouse_shape.zig.