feat: 약품별 선호 도매상 API + delivery_schedules 테이블

- GET /api/order/drug/{code}/preferred-vendor: 약품별 선호 도매상 조회
- POST /api/order/drugs/preferred-vendors: 일괄 조회
- MSSQL 입고장 데이터 활용 (WH_main, WH_sub)
- 최근 주문 도매상 + 최다 주문 도매상 반환

DB:
- delivery_schedules 테이블 생성 (orders.db)
- 도매상별 주문 마감시간/배송 도착시간 관리

backend/order_api.py

@@ -1227,3 +1227,163 @@ def api_update_wholesaler_limit(wholesaler_id):
         'success': True,
         'message': f'{wholesaler_id} 한도 업데이트 완료'
     })
+
+
+# ========== 약품별 선호 도매상 API ==========
+
+def get_drug_preferred_vendor(drug_code: str, period_days: int = 365):
+    """
+    약품코드 기준 선호 도매상 조회 (MSSQL 입고장 데이터)
+    """
+    import pyodbc
+    
+    CONN_STR = (
+        'DRIVER={ODBC Driver 17 for SQL Server};'
+        'SERVER=192.168.0.4\\PM2014;'
+        'DATABASE=PM_DRUG;'
+        'UID=sa;'
+        'PWD=tmddls214!%(;'
+        'TrustServerCertificate=yes;'
+        'Connection Timeout=10'
+    )
+    
+    try:
+        conn = pyodbc.connect(CONN_STR, timeout=10)
+        cursor = conn.cursor()
+        
+        # 약품명 조회
+        cursor.execute("SELECT GoodsName FROM CD_GOODS WHERE DrugCode = ?", drug_code)
+        row = cursor.fetchone()
+        drug_name = row[0] if row else ''
+        
+        # 도매상별 입고 통계
+        query = """
+        SELECT 
+            c.CD_NM_custom AS vendor_name,
+            c.CD_CD_custom AS vendor_code,
+            COUNT(*) AS order_count,
+            SUM(ws.WH_NM_item_a) AS total_qty,
+            SUM(ws.WH_MY_amount_a) AS total_amount,
+            AVG(ws.WH_MY_unit_a) AS avg_unit_price,
+            MAX(wm.WH_DT_appl) AS last_order_date
+        FROM WH_sub ws
+        JOIN WH_main wm ON ws.WH_SR_stock = wm.WH_NO_stock
+        LEFT JOIN PM_BASE.dbo.CD_custom c ON wm.WH_CD_cust_sale = c.CD_CD_custom
+        WHERE ws.DrugCode = ?
+          AND wm.WH_DT_appl >= CONVERT(varchar(8), DATEADD(day, ?, GETDATE()), 112)
+        GROUP BY c.CD_NM_custom, c.CD_CD_custom
+        ORDER BY COUNT(*) DESC
+        """
+        
+        cursor.execute(query, (drug_code, -period_days))
+        rows = cursor.fetchall()
+        
+        if not rows:
+            conn.close()
+            return {
+                'success': True,
+                'drug_code': drug_code,
+                'drug_name': drug_name,
+                'recent_vendor': None,
+                'most_frequent_vendor': None,
+                'vendors': [],
+                'message': '입고 이력 없음'
+            }
+        
+        vendors = []
+        for r in rows:
+            vendors.append({
+                'vendor_name': r[0] or '알수없음',
+                'vendor_code': r[1] or '',
+                'order_count': r[2],
+                'total_qty': float(r[3] or 0),
+                'total_amount': float(r[4] or 0),
+                'avg_unit_price': float(r[5] or 0),
+                'last_order_date': r[6]
+            })
+        
+        most_frequent = vendors[0] if vendors else None
+        
+        # 최근 주문 도매상
+        recent_query = """
+        SELECT TOP 1
+            c.CD_NM_custom AS vendor_name,
+            c.CD_CD_custom AS vendor_code,
+            wm.WH_DT_appl AS order_date,
+            ws.WH_NM_item_a AS qty,
+            ws.WH_MY_unit_a AS unit_price
+        FROM WH_sub ws
+        JOIN WH_main wm ON ws.WH_SR_stock = wm.WH_NO_stock
+        LEFT JOIN PM_BASE.dbo.CD_custom c ON wm.WH_CD_cust_sale = c.CD_CD_custom
+        WHERE ws.DrugCode = ?
+        ORDER BY wm.WH_DT_appl DESC
+        """
+        cursor.execute(recent_query, drug_code)
+        recent_row = cursor.fetchone()
+        
+        recent_vendor = None
+        if recent_row:
+            recent_vendor = {
+                'vendor_name': recent_row[0] or '알수없음',
+                'vendor_code': recent_row[1] or '',
+                'order_date': recent_row[2],
+                'qty': float(recent_row[3] or 0),
+                'unit_price': float(recent_row[4] or 0)
+            }
+        
+        conn.close()
+        
+        return {
+            'success': True,
+            'drug_code': drug_code,
+            'drug_name': drug_name,
+            'recent_vendor': recent_vendor,
+            'most_frequent_vendor': most_frequent,
+            'vendors': vendors
+        }
+        
+    except Exception as e:
+        return {
+            'success': False,
+            'error': str(e),
+            'drug_code': drug_code
+        }
+
+
+@order_bp.route('/drug/<drug_code>/preferred-vendor', methods=['GET'])
+def api_drug_preferred_vendor(drug_code):
+    """
+    약품별 선호 도매상 조회 API
+    
+    GET /api/order/drug/670400830/preferred-vendor
+    GET /api/order/drug/670400830/preferred-vendor?period=180
+    """
+    period = request.args.get('period', 365, type=int)
+    result = get_drug_preferred_vendor(drug_code, period)
+    return jsonify(result)
+
+
+@order_bp.route('/drugs/preferred-vendors', methods=['POST'])
+def api_drugs_preferred_vendors():
+    """
+    여러 약품의 선호 도매상 일괄 조회
+    
+    POST /api/order/drugs/preferred-vendors
+    {"drug_codes": ["670400830", "654301800"], "period": 365}
+    """
+    data = request.get_json() or {}
+    drug_codes = data.get('drug_codes', [])
+    period = data.get('period', 365)
+    
+    if not drug_codes:
+        return jsonify({'success': False, 'error': 'drug_codes required'})
+    
+    results = {}
+    for code in drug_codes:
+        results[code] = get_drug_preferred_vendor(code, period)
+    
+    return jsonify({
+        'success': True,
+        'count': len(results),
+        'results': results
+    })