[Frontend] Fix Recharts tooltip typing in RateHistoryChart

## Problem

The custom tooltip destructures payload and label from an incompatible generic type.

## Relevant code

`src/components/Rate/RateHistoryChart.tsx`

## Proposed scope

Use the supported tooltip content props, handle empty payloads, and test currency/date formatting for hover data.

## Acceptance criteria

- [ ] The reported behavior is reproduced or characterized with a focused automated test before the fix.
- [ ] The implementation satisfies the proposed scope without weakening TypeScript, lint, authorization, privacy, or error handling.
- [ ] Success, empty/loading where applicable, failure, and boundary cases are covered.
- [ ] Existing related tests pass and new regression coverage is included.
- [ ] User-facing behavior remains accessible by keyboard and at mobile viewport sizes where UI is affected.
- [ ] Documentation is updated when the change alters configuration, contracts, security assumptions, or contributor workflow.

## Contributor notes

Base the work on the latest `main` branch. Keep unrelated refactors out of the pull request and include screenshots or recordings for visible changes. Never use real pet, medical, contact, wallet, or credential data in fixtures.

Start in src/components/Rate/RateHistoryChart.tsx and inspect the custom tooltip's Recharts props and current formatting behavior. Reproduce or characterize the typing and hover-data issue with a focused automated test, then cover currency/date formatting and empty payloads. Done means the supported tooltip props are used, related tests pass, and regression coverage includes the stated boundary cases.

Written by the indexing model from the issue text.