assistant2: Adjust "Recent" header label design in context picker (#23364)

Just a little design fine-tune.

| Before | After |
|--------|--------|
| <img width="454" alt="Screenshot 2025-01-20 at 12 13 10 PM"
src="https://github.com/user-attachments/assets/b27372f2-00f5-40f4-927d-0d831ec4b90d"
/> | <img width="454" alt="Screenshot 2025-01-20 at 12 12 17 PM"
src="https://github.com/user-attachments/assets/207d08da-d75e-4c60-a6eb-cb1549b5925c"
/> |

Release Notes:

- N/A
40a6b0a0a3Danilo Leal committed on 1/20/2025, 3:42:05 PM· committed by GitHubparent919803a
1 file changedLine totals unavailable