fix: _CHUNK 1500→1200 — asyncpg 32767 param limit 방지

26 cols × 1500 = 39000 > 32767로 MSTR/COIN/META/GOOGL 등 대형 filer에서 batch insert 실패.
26 cols × 1200 = 31200으로 안전하게 유지.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/services/insider_transaction_service.py

@@ -22,7 +22,7 @@ from app.services.sec_full_index_service import IndexEntry
 logger = logging.getLogger(__name__)
 
 # Chunk size for batch insert (asyncpg 32767-param limit)
-_CHUNK = 1500  # ~22 cols × 1500 = 33000 → stay under 32767 with ~20 populated
+_CHUNK = 1200  # 26 cols × 1200 = 31200 → safely under asyncpg 32767-param limit
 
 # C-suite title regex patterns (case-insensitive)
 _RE_CEO = re.compile(r"\b(CEO|Chief\s+Executive\s+Officer)\b", re.IGNORECASE)