fix: 修复 sim_trade/smart_trade 未导入 put_db 导致 NameError 和连接泄漏

- sim_trade.py: 导入 put_db（之前使用了但未导入，每次 finally 都会 NameError）
- smart_trade.py: 同上，9处 put_db 调用因未导入而失效
- sim_trade.py: trigger_trade 智能引擎异常时 conn 泄漏，改用 finally 确保归还

stock-html/routes/sim_trade.py

@@ -4,7 +4,7 @@
 """
 from flask import Blueprint, request, jsonify
 from datetime import datetime, date, time
-from db import get_db, login_required, get_current_user_id
+from db import get_db, put_db, login_required, get_current_user_id
 from psycopg2.extras import RealDictCursor
 
 bp = Blueprint('sim_trade', __name__, url_prefix='/api/sim')
@@ -623,12 +623,12 @@ def trigger_trade():
     
     try:
         # 优先使用智能引擎
+        smart_conn = None
         try:
             from services.smart_trade_engine import execute_smart_trade
-            conn = get_db()
-            if conn:
-                result = execute_smart_trade(conn, user_id, scan_date=None)
-                put_db(conn)
+            smart_conn = get_db()
+            if smart_conn:
+                result = execute_smart_trade(smart_conn, user_id, scan_date=None)
                 if result.get('success'):
                     results = result.get('results', [])
                     buy_count = len([r for r in results if r['type'] == 'buy'])
@@ -641,6 +641,9 @@ def trigger_trade():
                     })
         except Exception as e:
             print(f"[trigger_trade] 智能引擎异常，降级: {e}")
+        finally:
+            if smart_conn:
+                put_db(smart_conn)
         
         # 降级: 使用旧引擎
         from services.scheduler import execute_auto_trade_for_user

stock-html/routes/smart_trade.py

@@ -4,7 +4,7 @@
 """
 from flask import Blueprint, request, jsonify
 from datetime import date
-from db import get_db, login_required, get_current_user_id
+from db import get_db, put_db, login_required, get_current_user_id
 from psycopg2.extras import RealDictCursor
 
 bp = Blueprint('smart_trade', __name__, url_prefix='/api/smart')