EpcClientService.search_by_postcode already returns the matched
certificate number alongside the UPRN, but it was dropped before
persistence. Thread it through get_epc_data_with_postcode ->
get_uprn_with_epc_df / get_uprn_from_historic_epc (using the historic
dataset's lmk_key) -> the address2uprn_certificate_number result
column -> PropertyIdentityInsert -> the property table's new
certificate_number column (assessment-model PR #362).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>