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-TW.json

@@ -646,6 +646,7 @@
       "subId": "訂閱 ID",
       "online": "上線",
       "email": "電子郵件",
+      "emailInvalidChars": "電子郵件不能包含空格、'/'、'\\' 或控制字元",
       "group": "群組",
       "groupDesc": "用於將相關客戶端歸類的邏輯標籤(如團隊、客戶、地區)。可從工具列篩選。",
       "groupPlaceholder": "如 customer-a",