Serial No.cosmetic_grade is empty on production. The actual C# data lives
in Device Condition Report (42,940 records). Updated script to lookup
latest report per serial_no and map from there.
Run after bench migrate. Maps cosmetic_grade C# values to new grade field:
- C5-C9 → High
- C4 → Med
- C3 → Low
- C0-C2, blank → Flagged
Requires: bench migrate has already created the new fields.