Fix 14 malformed/corrupted `LineItem` date values in ground truth (3 documents)
## Summary
While using this dataset to benchmark key-information-extraction accuracy, we
found that `LineItems` scores were being capped by a small number of **corrupted
date strings in the ground-truth labels** rather than by model behavior. This PR
corrects **14 malformed date values across 3 documents**. Every correction is
verified against the source PDF image and preserves the original digit content.
No other values are changed. No document's set of rows is added to or removed
from. This is a surgical typo fix.
## Documents & changes
| Document | Row | Field | Current | Proposed | Rationale |
|---|---|---|---|---|---|
| `3b768c37cd4670c0f28b0e89d7507e05` | 12 | EndDate | `11/0316` | `11/03/16` | Missing `/`; every row in this invoice has StartDate == EndDate, both `11/03/16` |
| `d1a83bbb1eeb256a325dab9e0ce6235b` | 206,219,220 | StartDate | `2.7.16` | `2-7-16` | Invoice renders all dates as `M-D-Y…
