fix: maxDuration 60 → 300 for Fluid Compute

maxDuration=60 was overriding Fluid Compute's 300s limit.
Gemini generateContent with thinking+search takes ~12s/call.
BATCH_SIZE=5 (10 calls) needs ~120s.

Author: Miriad

app/api/cron/check-research/route.ts

@@ -1,5 +1,5 @@
 export const fetchCache = 'force-no-store';
-export const maxDuration = 60;
+export const maxDuration = 300; // Fluid Compute enabled
 
 import { type NextRequest } from 'next/server';
 import { createClient, type SanityClient } from 'next-sanity';