feat(inbounds): bulk-attach & assign-group client actions + form defaults

- Bulk-attach an inbound's clients onto other inbounds (same identity, shared traffic): new ClientService.BulkAttach + POST /clients/bulkAttach, an inbound row action, and AttachClientsModal.
- Assign all of an inbound's clients to a group from the inbound page, reusing /clients/bulkAssignGroup and the existing BulkAssignGroupModal.
- Default a random user/pass account for new Mixed and HTTP inbounds instead of an empty accounts list.
- Capitalize the inbound Security toggle labels (None/TLS/Reality).

frontend/src/pages/inbounds/InboundFormModal.tsx

@@ -2473,9 +2473,9 @@ export default function InboundFormModal({
                 disabled={!tlsOk}
                 onChange={(e) => onSecurityChange(e.target.value)}
               >
-                {!tlsOnly && <Radio.Button value="none">none</Radio.Button>}
-                <Radio.Button value="tls">tls</Radio.Button>
-                {realityOk && <Radio.Button value="reality">reality</Radio.Button>}
+                {!tlsOnly && <Radio.Button value="none">None</Radio.Button>}
+                <Radio.Button value="tls">TLS</Radio.Button>
+                {realityOk && <Radio.Button value="reality">Reality</Radio.Button>}
               </Radio.Group>
             );
           }}