fix: reduce INFOGRAPHIC_BATCH_SIZE to 2 for Gemini generateContent timing

Gemini generateContent with thinking+search grounding takes ~12s/call
vs ~4s for Imagen. BATCH_SIZE=4 (8 calls) exceeds Vercel 60s limit.
BATCH_SIZE=2 (4 calls × ~12s = ~48s) fits safely.

Author: Miriad

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

@@ -118,7 +118,7 @@ async function buildStuckThresholds(): Promise<Record<string, number>> {
 const MAX_DOCS_PER_STATUS = 2;
 
 /** Max prompts to process per cron cycle (each prompt = 2 Imagen calls) */
-const INFOGRAPHIC_BATCH_SIZE = 4;
+const INFOGRAPHIC_BATCH_SIZE = 2; // Gemini generateContent with thinking+search takes ~12s/call
 
 // ---------------------------------------------------------------------------
 // Sanity Write Client