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.

frontend/src/pages/api-docs/endpoints.ts

@@ -607,6 +607,25 @@ export const sections: readonly Section[] = [
         summary: 'Delete every client whose traffic quota is exhausted (used >= total, when reset is disabled) or whose expiry has passed. Returns the deleted count and triggers an Xray restart when any client was on a running inbound.',
         response: '{\n  "success": true,\n  "obj": {\n    "deleted": 0\n  }\n}',
       },
+      {
+        method: 'POST',
+        path: '/panel/api/clients/delOrphans',
+        summary: 'Delete every client that is not attached to any inbound, along with its traffic record, IP log, and external links. Useful for clearing clients left unattached after their inbounds were removed. Returns the deleted count. Cannot be undone.',
+        response: '{\n  "success": true,\n  "obj": {\n    "deleted": 0\n  }\n}',
+      },
+      {
+        method: 'GET',
+        path: '/panel/api/clients/export',
+        summary: 'Return every client as a {client, inboundIds} array — the same shape /bulkCreate and /import accept — so the payload round-trips straight back through /import. Clients with no inbound attachment are included with an empty inboundIds list. The UI shows this in a CodeMirror viewer (copy / download); programmatic callers get the array in obj.',
+        response: '{\n  "success": true,\n  "obj": [\n    {\n      "client": {\n        "email": "alice@example.com",\n        "id": "...",\n        "totalGB": 53687091200,\n        "expiryTime": 0,\n        "enable": true,\n        "subId": "..."\n      },\n      "inboundIds": [7, 9]\n    }\n  ]\n}',
+      },
+      {
+        method: 'POST',
+        path: '/panel/api/clients/import',
+        summary: 'Import clients from a JSON body { "data": "<json>" }, where data is a string-encoded array produced by /export ([{client, inboundIds}]). Items with inboundIds are created and attached to those inbounds; items with an empty inboundIds list are restored as unattached client records. Existing emails are never overwritten — they are returned in skipped. Triggers a single Xray restart at the end if any target inbound was running.',
+        body: '{\n  "data": "[{\\"client\\":{\\"email\\":\\"alice@example.com\\",\\"enable\\":true},\\"inboundIds\\":[7]}]"\n}',
+        response: '{\n  "success": true,\n  "obj": {\n    "created": 2,\n    "skipped": [\n      { "email": "alice@example.com", "reason": "email already in use: alice@example.com" }\n    ]\n  }\n}',
+      },
       {
         method: 'POST',
         path: '/panel/api/clients/bulkAdjust',