feat(clients): allow attaching clients to socks/mixed inbounds

The client form, bulk-add form and the inbound-side attach entry all
filtered attachable inbounds by a protocol whitelist that lacked
socks/mixed (inherited from upstream), so SK5 inbounds could never be
picked as a client's associated inbound even though the backend
accepts the association. Add 'socks' and 'mixed' to all three gates.
The client record's existing password field is the socks credential;
no new credential shape is introduced.

frontend/src/pages/clients/ClientBulkAddModal.tsx

@@ -37,6 +37,8 @@ const MULTI_CLIENT_PROTOCOLS = new Set([
   'hysteria',
   'wireguard',
   'amneziawg',
+  'socks',
+  'mixed',
 ]);
 
 const EMPTY: ClientBulkAddFormValues = {

frontend/src/pages/clients/ClientFormModal.tsx

@@ -61,6 +61,8 @@ const MULTI_CLIENT_PROTOCOLS = new Set([
   'wireguard',
   'mtproto',
   'amneziawg',
+  'socks',
+  'mixed',
 ]);
 
 const CLIENT_FORM_MODAL_Z_INDEX = 1000;

frontend/src/pages/inbounds/list/helpers.ts

@@ -90,6 +90,8 @@ export function isInboundMultiUser(record: { protocol: string; settings: unknown
     case 'mtproto':
     case 'wireguard':
     case 'amneziawg':
+    case 'socks':
+    case 'mixed':
       return true;
     case 'shadowsocks':
       return isSSMultiUser({ protocol: 'shadowsocks', settings: readSettings(record.settings) });