feat: replace grok-4 with grok-3-fast

dev.log

@@ -0,0 +1,13 @@
+$ next dev --turbo
+   ▲ Next.js 15.5.4 (Turbopack)
+   - Local:        http://localhost:3000
+   - Network:      http://192.168.0.2:3000
+   - Environments: .env
+   - Experiments (use with caution):
+     · serverActions
+
+ ✓ Starting...
+Attention: Next.js now collects completely anonymous telemetry regarding usage.
+This information is used to shape Next.js' roadmap and prioritize features.
+You can learn more, including how to opt-out if you'd not like to participate in this anonymous program, by visiting the following URL:
+https://nextjs.org/telemetry

lib/utils/index.ts

@@ -30,7 +30,7 @@ export function getModel() {
     })
     // Optionally, add a check for credit status or skip xAI if credits are exhausted
     try {
-      return xai('grok-4-fast-non-reasoning')
+      return xai('grok-3-fast')
     } catch (error) {
       console.warn('xAI API unavailable, falling back to OpenAI:')
     }