Eliminates white flash by deferring window show until paint

Defers Electron window display until the renderer signals first
meaningful paint, avoiding initial blank screens or white flashes,
especially on startup and settings windows. Implements a handshake
using a renderer-to-main process message, color-matches background
to the current theme, and falls back to a timeout in development.

Also migrates font loading to npm packages, replaces Google Fonts
usage, and adds code-splitting for dialogs and quick switcher to
improve performance. Restricts console debug output to development.

index.tsx

@@ -1,9 +1,17 @@
+import { Suspense, lazy } from 'react';
 import ReactDOM from 'react-dom/client';
-import '@xterm/xterm/css/xterm.css';
+import '@fontsource/space-grotesk/400.css';
+import '@fontsource/space-grotesk/500.css';
+import '@fontsource/space-grotesk/600.css';
+import '@fontsource/space-grotesk/700.css';
+import '@fontsource/jetbrains-mono/400.css';
+import '@fontsource/jetbrains-mono/500.css';
+import '@fontsource/jetbrains-mono/600.css';
 import App from './App';
-import SettingsPage from './components/SettingsPage';
 import { ToastProvider } from './components/ui/toast';
 
+const LazySettingsPage = lazy(() => import('./components/SettingsPage'));
+
 const rootElement = document.getElementById('root');
 if (!rootElement) {
   throw new Error("Could not find root element to mount to");
@@ -25,7 +33,9 @@ const renderApp = () => {
   if (route === 'settings') {
     root.render(
       <ToastProvider>
-        <SettingsPage />
+        <Suspense fallback={null}>
+          <LazySettingsPage />
+        </Suspense>
       </ToastProvider>
     );
   } else {