fix(clients): reject spaces, '/', '\' and control chars in client email

Client emails containing a slash broke the path-param routes
(edit/delete/view returned 404 / "client not found"), leaving stale
records that could only be cleared with manual SQLite edits. Validate
the email on both the backend (Create + Update, which also covers the
bulk paths) and the frontend (Zod) so these characters are rejected at
save time with a clear, localized message across all 13 locales.

Closes #4695

web/translation/zh-CN.json

@@ -646,6 +646,7 @@
       "subId": "订阅 ID",
       "online": "在线",
       "email": "邮箱",
+      "emailInvalidChars": "邮箱不能包含空格、'/'、'\\' 或控制字符",
       "group": "分组",
       "groupDesc": "用于对相关客户端进行分桶的逻辑标签（如团队、客户、地区）。可从工具栏筛选。",
       "groupPlaceholder": "如 customer-a",