perf: 优化管理后台性能 - 修复N+1查询、添加索引、优化统计

- 修复NewsAdmin的N+1查询问题，使用joinedload预加载
- 添加数据库索引迁移脚本（Site、News、Tag表）
- 优化管理后台统计查询，减少数据传输

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

migrations/add_performance_indexes.py

@@ -0,0 +1,71 @@
+"""
+数据库索引优化迁移脚本
+为Site、News表的高频查询字段添加索引，提升查询性能
+
+执行方式: python migrations/add_performance_indexes.py
+"""
+import os
+import sys
+
+# 添加项目根目录到路径
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from app import create_app, db
+from models import Site, News, Tag
+
+
+def add_indexes():
+    """添加性能优化索引"""
+    app = create_app('development')
+
+    with app.app_context():
+        # 检查并添加索引
+        indexes_to_add = [
+            # Site表索引
+            ('idx_site_is_active', 'sites', 'is_active'),
+            ('idx_site_created_at', 'sites', 'created_at'),
+            ('idx_site_view_count', 'sites', 'view_count'),
+            ('idx_site_is_recommended', 'sites', 'is_recommended'),
+            ('idx_site_sort_order', 'sites', 'sort_order'),
+
+            # News表索引
+            ('idx_news_site_id', 'news', 'site_id'),
+            ('idx_news_is_active', 'news', 'is_active'),
+            ('idx_news_published_at', 'news', 'published_at'),
+            ('idx_news_created_at', 'news', 'created_at'),
+
+            # Tag表索引
+            ('idx_tag_sort_order', 'tags', 'sort_order'),
+        ]
+
+        for index_name, table_name, column_name in indexes_to_add:
+            try:
+                # 检查索引是否已存在
+                check_sql = f"""
+                    SELECT COUNT(*) as count
+                    FROM information_schema.STATISTICS
+                    WHERE TABLE_SCHEMA = DATABASE()
+                    AND TABLE_NAME = '{table_name}'
+                    AND INDEX_NAME = '{index_name}'
+                """
+                result = db.session.execute(db.text(check_sql)).fetchone()
+
+                if result[0] == 0:
+                    # 创建索引
+                    db.session.execute(db.text(
+                        f"CREATE INDEX {index_name} ON {table_name}({column_name})"
+                    ))
+                    print(f"✓ 添加索引: {index_name} ON {table_name}({column_name})")
+                else:
+                    print(f"- 索引已存在: {index_name}")
+
+            except Exception as e:
+                print(f"✗ 添加索引失败 {index_name}: {str(e)}")
+
+        # 提交更改
+        db.session.commit()
+        print("\n索引优化完成！")
+
+
+if __name__ == '__main__':
+    add_indexes()