Import Validation Issue Override Value

When a compliance reviewer resolves an ImportValidationIssue, they can either accept Piper's suggestion or type their own correction into the overrideValue field. This override is then used instead of the original value from the lab file when the row is committed as an AnalyticalResult. Recording the overrideValue separately from the original value field ensures full audit traceability — both the bad original data and the human-approved correction are preserved, documenting the data quality decision made before the result entered the permanent monitoring record.