feat(inbounds): attach existing clients to an inbound in one click

Adds an 'Attach Existing Clients' row action on multi-user inbounds (shown even when the inbound is empty). It opens a modal listing the whole client pool with search and group filter, all attachable clients pre-selected, and attaches the selection to that inbound via the existing bulkAttach endpoint. Clients already on the inbound are shown disabled and skipped. Translations added for all 13 locales.

web/translation/id-ID.json

@@ -320,6 +320,11 @@
       "attachClientsSearchPlaceholder": "Cari email atau komentar",
       "attachClientsStatusDisabled": "Dinonaktifkan",
       "attachClientsSelectedCount": "{selected} dari {total} dipilih",
+      "attachExistingClients": "Lampirkan klien yang ada…",
+      "attachExistingTitle": "Lampirkan klien yang ada ke «{remark}»",
+      "attachExistingDesc": "Melampirkan klien yang ada ({count} tersedia) ke inbound ini — UUID/kata sandi sama dan trafik bersama. Klien yang sudah ada di sini dilewati.",
+      "attachExistingNoClients": "Belum ada klien. Buat klien dulu, lalu lampirkan di sini.",
+      "attachExistingStatusAttached": "Sudah dilampirkan",
       "detachClients": "Lepas klien",
       "detachClientsTitle": "Lepas klien dari «{remark}»",
       "detachClientsDesc": "Menghapus klien terpilih hanya dari inbound ini. Catatan klien tetap dipertahankan (gunakan Delete untuk menghapus sepenuhnya). Sumber memiliki total {count} klien.",