feat: update loading message duration and add caching information; increase timeout for theme session generation

src/components/theme_session/ThemeSessionView.jsx

@@ -45,7 +45,7 @@ export default function ThemeSessionView({
       <Card className="w-full text-center py-16">
         <Loader size={48} className="mx-auto text-teal animate-spin mb-4" />
         <p className="font-medium text-lg">Preparing this week's theme session…</p>
-        <p className="text-fg-muted text-sm mt-2">This may take 15–30 seconds the first time.</p>
+        <p className="text-fg-muted text-sm mt-2">This may take 30–90 seconds the first time — the result is cached.</p>
       </Card>
     );
   }