macOS application menu

Standard menus (App: hide/quit; Edit: clipboard roles enabling Cmd+C/V/X/Z;
View: Refresh Cmd+R + fullscreen; Window: minimize/zoom/cycle) plus File with
New/Close Tab (Cmd+T/W), New Folder/File, and a Connect submenu built from
saved connections (folders as nested submenus, Connection Manager entry).
Custom actions forward to the webview as menuAction messages; the menu rebuilds
whenever connections change. macOS-only per electrobun support.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/shared/rpc.ts

@@ -82,6 +82,7 @@ export type AppRPC = {
 		messages: {
 			transferUpdate: TransferSnapshot;
 			sessionClosed: { sessionId: string; reason: string };
+			menuAction: { action: string };
 		};
 	};
 };