fix: fetch_and_store_bars() interval 컬럼 추가 + CHUNK 분할

- interval 누락으로 uq_alpaca_price_data constraint 위반 방지
- 단일 INSERT → CHUNK=2300 분할 (14 params/row, asyncpg 한도 대비)

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

app/services/alpaca_price_service.py

@@ -61,6 +61,7 @@ class AlpacaPriceService:
             rows.append({
                 "ticker": ticker,
                 "date": bar_dt,
+                "interval": interval,
                 "open": float(bar.get("o", 0)),
                 "high": float(bar.get("h", 0)),
                 "low": float(bar.get("l", 0)),
@@ -74,13 +75,16 @@ class AlpacaPriceService:
         if not rows:
             return 0
 
-        # Batch insert — skip duplicates via ON CONFLICT DO NOTHING
-        stmt = pg_insert(AlpacaPriceData).values(rows)
+        # Batch insert with chunking (14 params/row → CHUNK=2300, 2300×14=32,200 < 32,767)
+        CHUNK = 2300
+        inserted = 0
+        for i in range(0, len(rows), CHUNK):
+            stmt = pg_insert(AlpacaPriceData).values(rows[i : i + CHUNK])
             stmt = stmt.on_conflict_do_nothing(constraint='uq_alpaca_price_data')
             result = await db.execute(stmt)
+            inserted += result.rowcount
         await db.commit()
 
-        inserted = result.rowcount
         if inserted:
             logger.info(f"Alpaca: inserted {inserted} bars for {ticker}")