fix: add error handling and local dev fallback for auth

- Handle getAccessToken failure gracefully
- Support LLM_API_TOKEN env var for local dev (bypasses OAuth)
- Better error messages for missing credentials

app/api/chat/route.ts

@@ -135,9 +135,19 @@ GOOD example:
 BAD: "Rock resolved the Terraform configuration drift issue by implementing automated drift detection and real-time visibility into discrepancies..." — this is garbage. Never do this.`
 
 export async function POST(request: NextRequest) {
+  let token: string
+  
+  try {
+    token = await getAccessToken()
+  } catch (error) {
+    console.error('Failed to get access token:', error)
+    return new Response(
+      JSON.stringify({ error: 'Authentication failed - check AUTHENTIK_CLIENT_ID/SECRET' }),
+      { status: 500, headers: { 'Content-Type': 'application/json' } }
+    )
+  }
+
   try {
-    // Get OAuth token (cached, auto-refreshes)
-    const token = await getAccessToken()
     const { message } = await request.json()
 
     const response = await fetch(LLM_API_URL, {