feat: 添加邮件功能第四阶段 - 任务完成通知

1. 添加任务完成邮件模板 (templates/email/task_complete.html)
2. 在email_service.py中添加:
   - task_notify_enabled 字段支持
   - send_task_complete_email() 函数，支持附件大小限制和分批发送
   - send_task_complete_email_async() 异步发送函数
   - MAX_ATTACHMENT_SIZE 常量 (10MB)
3. 更新app.py:
   - 邮件设置API支持task_notify_enabled字段
   - 截图回调中集成任务完成邮件发送
4. 更新admin.html:
   - 添加"启用任务完成通知"开关
   - 更新loadEmailSettings/updateEmailSettings函数

附件超过10MB时会自动分两封邮件发送（通知+截图），作为容错机制

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app.py

@@ -2487,11 +2487,11 @@ def take_screenshot_for_account(user_id, account_id, browse_type="应读", sourc
             # 重置账号状态
             account.is_running = False
             account.status = "未开始"
-            
+
             # 先清除任务状态（这样to_dict()不会包含detail_status）
             if account_id in task_status:
                 del task_status[account_id]
-            
+
             # 然后发送更新
             socketio.emit('account_update', account.to_dict(), room=f'user_{user_id}')
 
@@ -2517,6 +2517,29 @@ def take_screenshot_for_account(user_id, account_id, browse_type="应读", sourc
                     source=source
                 )
 
+                # 发送任务完成邮件通知
+                try:
+                    user_info = database.get_user_by_id(user_id)
+                    if user_info and user_info.get('email'):
+                        screenshot_path = None
+                        if result and result.get('success') and result.get('filename'):
+                            screenshot_path = os.path.join(SCREENSHOTS_DIR, result['filename'])
+
+                        account_name = account.remark if account.remark else account.username
+                        email_service.send_task_complete_email_async(
+                            user_id=user_id,
+                            email=user_info['email'],
+                            username=user_info['username'],
+                            account_name=account_name,
+                            browse_type=browse_type,
+                            total_items=browse_result.get('total_items', 0),
+                            total_attachments=browse_result.get('total_attachments', 0),
+                            screenshot_path=screenshot_path,
+                            log_callback=lambda msg: log_to_client(msg, user_id, account_id)
+                        )
+                except Exception as email_error:
+                    logger.warning(f"发送任务完成邮件失败: {email_error}")
+
         except Exception as e:
             logger.error(f"截图回调出错: {e}")
 
@@ -3716,12 +3739,14 @@ def update_email_settings_api():
         failover_enabled = data.get('failover_enabled', True)
         register_verify_enabled = data.get('register_verify_enabled')
         base_url = data.get('base_url')
+        task_notify_enabled = data.get('task_notify_enabled')
 
         email_service.update_email_settings(
             enabled=enabled,
             failover_enabled=failover_enabled,
             register_verify_enabled=register_verify_enabled,
-            base_url=base_url
+            base_url=base_url,
+            task_notify_enabled=task_notify_enabled
         )
         return jsonify({'success': True})
     except Exception as e: