refactor: split every monolithic module into focused submodules

Each source file that had grown beyond a single concern is replaced by an identically-named directory containing focused submodules. `src/event_loop/mod.rs` (878 lines) becomes a directory with clipboard, context_menu, cursor_shape, drag, focus, handlers, invalidation, overlays_reconcile, repeat, run, surface, text_editing, and tooltip. Every widget, input handler, and theme component follows the same split. Public interfaces are unchanged — only the internal file layout moves.
image bumped from 0.25.2 to 0.25.9.

benches/lookup.rs

@@ -41,6 +41,8 @@ fn build_widgets( n: usize ) -> Vec<LaidOutWidget<()>>
 			paint_rect:         rect,
 			handlers,
 			keyboard_focusable: true,
+			cursor:             ltk::CursorShape::Default,
+			tooltip:            None,
 		}
 	} ).collect()
 }