Sublime-style Build-n versioning + About box

Build n = commit count, baked at build time into a gitignored
version.gen.ts (postinstall + all build scripts regenerate it). About
lives in the macOS app menu and as a footer row in the options popover
(the cross-platform path), showing build, commit, date and engines.

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

src/bun/rpc-handlers.ts

@@ -30,6 +30,7 @@ export interface AppDeps {
 		openEditor: (ctx: EditorOpenContext) => void;
 		settingsChanged: (settings: AppSettings) => void;
 		openConnectionManager: () => void;
+		showAbout: () => void;
 	};
 }
 
@@ -294,6 +295,12 @@ export function createAppRPC({
 						events.openConnectionManager();
 						return {};
 					}),
+
+				showAbout: () =>
+					wrap(async () => {
+						events.showAbout();
+						return {};
+					}),
 			},
 		},
 	});