chore(renderer): default to light theme

User prefers light mode. next-themes previously defaulted to dark
which made first-load users (no localStorage) see a dark UI. With
'enableSystem' on, 'system' is still available as a choice — only
the initial value changed.

Existing users with 'dark' in localStorage keep dark until they toggle.
New users get light.

src/renderer/main.tsx

@@ -6,7 +6,7 @@ import './styles/globals.css';
 
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <React.StrictMode>
-    <ThemeProvider defaultTheme="dark" attribute="class" enableSystem>
+    <ThemeProvider defaultTheme="light" attribute="class" enableSystem>
       <App />
     </ThemeProvider>
   </React.StrictMode>