Track wire roll serial number extraction source in `wire_set_certs` table

[rhythmatician]

When parsing certificate documents, the wire roll serial number (wire_roll_cert_number) can come from different sources depending on the workbook format:

• Old-format workbooks: CERT, Wire Roll sheet, cell B6
• New-format workbooks: Order Info sheet, cell B3

Currently we log which source was used, but this information isn't persisted. Adding a wire_source column (or similar) to the wire_set_certs table would let us:

1. Audit/debug — quickly determine where a wire roll SN came from without re-parsing the document
2. Detect format drift — identify if workbook formats are changing over time
3. Extend to other fields — the same pattern could track the source of traceability_number (cell B11 vs. content-disposition filename) and service_date (Excel H15 vs. PDF OCR vs. Qualer service record)

Current code reference: The TODO is on parse.py, where wire_source is set to a descriptive string but only used in log messages.

Suggested implementation:

• Add a nullable Text column (e.g. wire_roll_source) to wire_set_certs
• Populate it with the source string already being built in parse_certificate_data_excel (e.g. "sheet='CERT, Wire Roll', cell=B6")
• Consider whether to also track sources for traceability_number and service_date in the same migration