fix(synthesis): Select most common business_id to handle data leakage

Changed the business name query to ORDER BY COUNT(*) DESC instead of
arbitrary LIMIT 1, ensuring the correct business is identified even
when trace amounts of other business data leak into a job.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/reviewiq-pipeline/src/reviewiq_pipeline/stages/stage5_synthesize.py

@@ -486,10 +486,13 @@ class Stage5Synthesizer:
             ORDER BY negative DESC
         """, job_id)
 
-        # Business name
+        # Business name - get the most common one (in case of data leakage)
         business = await self.pool.fetchval("""
-            SELECT DISTINCT business_id FROM pipeline.reviews_enriched
-            WHERE job_id = $1::uuid LIMIT 1
+            SELECT business_id FROM pipeline.reviews_enriched
+            WHERE job_id = $1::uuid
+            GROUP BY business_id
+            ORDER BY COUNT(*) DESC
+            LIMIT 1
         """, job_id)
 
         # MOMENTUM: Calculate from data (not LLM guess)