agent_ui: Fix placeholder wrapping in the message editor (#55125)

Fixes this:

<img width="400" alt="image"
src="https://github.com/user-attachments/assets/6068009d-a0d4-4255-9fe1-16a41751806f"
/>

Release Notes:

- Fixed a bug where placeholder text in the agent panel's message editor
wouldn't properly wrap.
3014170d7eDanilo Leal committed on 4/28/2026, 11:31:31 PM· committed by GitHubparent42c9ac9
1 file changedLine totals unavailable