feat(ui): replace app-menu logo with a quick-access file toolbar

Remove the OCS-logo button and the dropdown menu it opened; the top strip
now shows direct New / Open / Save / Save As / Print buttons ahead of the
undo/redo controls. Drop the HELP and OPTIONS commands (HELP dumped text to
the command line, OPTIONS aliased the drafting-settings popup).

The app-menu overlay is gone, so its rendering code, MENU_ITEMS, four dead
messages, and the LOGO_RED / GEAR / HELP assets are removed. The recents
list it held is the only survivor — moved into OpenCADStudio.recent_files
via a new app/recent.rs, backing the Start page's Recent Documents panel.

Quick-access icons are redrawn in a cleaner style (file-plus, folder-open,
device-floppy, file-export, printer) and tinted light so they read on the
dark strip; FOLDER / DOC keep their old glyphs for the file browser.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/mod.rs

@@ -2,7 +2,6 @@
 /// Change this to scale the ribbon, layer manager rows, and property panel rows uniformly.
 pub const ROW_H: f32 = 26.0;
 
-pub mod app_menu;
 pub mod color_select;
 pub mod command_line;
 pub mod icons;
@@ -17,7 +16,6 @@ pub mod style;
 pub mod text_util;
 pub mod window;
 
-pub use app_menu::AppMenu;
 pub use command_line::CommandLine;
 pub use properties::PropertiesPanel;
 pub use ribbon::Ribbon;