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/ja-JP.json

@@ -646,6 +646,7 @@
       "subId": "サブスクリプション ID",
       "online": "オンライン",
       "email": "メール",
+      "emailInvalidChars": "メールアドレスにスペース、'/'、'\\'、または制御文字を含めることはできません",
       "group": "グループ",
       "groupDesc": "関連クライアントをまとめる論理ラベル(チーム、顧客、地域など)。ツールバーからフィルタ可能。",
       "groupPlaceholder": "例: customer-a",