feat(clients): orphan cleanup + export/import via CodeMirror modals

Add three client-management actions to the Clients page More menu:

- Delete unattached clients: removes every client with no inbound
  attachment, cascading its traffic rows, IP log, and external links
  (POST /clients/delOrphans).
- Export clients: shows the {client, inboundIds} list in a read-only
  CodeMirror viewer with copy/download (GET /clients/export returns the
  array in the standard envelope).
- Import clients: pastes that JSON into an editable CodeMirror editor,
  mirroring Import an Inbound (POST /clients/import takes a { data }
  body). Attached clients go through the create-and-attach path; items
  with no inboundIds are restored as bare records; existing emails are
  never overwritten and are reported as skipped.

Document the new endpoints in api-docs and translate the new strings
into all supported languages.

internal/web/translation/ar-EG.json

@@ -828,6 +828,12 @@
       "delDepleted": "حذف المنتهية",
       "delDepletedConfirmTitle": "حذف العملاء المنتهية حصصهم؟",
       "delDepletedConfirmContent": "يُحذف كل عميل استُنفِدت حصة حركة مروره أو انتهت صلاحيته. لا يمكن التراجع.",
+      "exportClients": "تصدير العملاء",
+      "importClients": "استيراد العملاء",
+      "import": "استيراد",
+      "delOrphans": "حذف العملاء غير المرتبطين",
+      "delOrphansConfirmTitle": "حذف العملاء بلا اتصال وارد؟",
+      "delOrphansConfirmContent": "يزيل كل عميل غير مرتبط بأي اتصال وارد مع سجل حركة مروره. لا يمكن التراجع.",
       "auth": "Auth",
       "hysteriaAuth": "Hysteria Auth",
       "uuid": "UUID",
@@ -850,7 +856,10 @@
         "bulkCreatedMixed": "تم إنشاء {ok}, وفشل {failed}",
         "bulkAdjusted": "تم تعديل {count} عميل",
         "bulkAdjustedMixed": "{ok} تم تعديلهم، {skipped} تم تخطيهم",
-        "delDepleted": "تم حذف {count} عميل منتهٍ"
+        "delDepleted": "تم حذف {count} عميل منتهٍ",
+        "delOrphans": "تم حذف {count} عميل غير مرتبط",
+        "imported": "تم استيراد {count} عميل",
+        "importedMixed": "{ok} تم استيرادهم، {failed} تم تخطيهم"
       }
     },
     "groups": {