Replaces the native list with a combobox (name/code/CNPJ search, accent- and
case-insensitive, keyboard + mouse, custom dropdown, hidden client_id = the
Gerenciador's real CLIENTE.ID). The backend resolves client_id against the
active GTI_GERENCIADOR mirror and rejects free text/unknown ids. Adds
Tenant.external_cnpj (migration 0025) mirrored via the internal endpoint.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>