agent_ui: Fix `@fetch` mention if URL contains `@` character (#51953)

## Context

Closes #47111

Release Notes:

- Fixed an issue where using `@fetch` in the agent panel would break if
URL contained an `@` character

Co-authored-by: Marshall Bowers <git@maxdeviant.com>
a3173c4d22Bennet Bo Fenner committed on 3/19/2026, 5:07:58 PM· committed by GitHubparented42b80
1 file changedLine totals unavailable