Component test: RecipientEditor warns on duplicate recipient addresses

[Spagero763]

Context

RecipientEditor's duplicate-recipient warning has no test coverage. See app/src/components/RecipientEditor.tsx.

Acceptance criteria

• A test adds the same recipient address twice and asserts the duplicate warning renders.

Per CONTRIBUTING.md: one concern, tests required for behaviour changes. CI gate: cargo fmt / cargo clippy --all-targets -- -D warnings / cargo test for Rust, npm run build for the sdk/app.

[Silver36-ship-it]

I would love to work on this professionally, please assign it to me

[adesuwa-tech]

Hi maintener, i would love to work one this issue, i already reviewed the description and will submit a clean PR, please kindly assign