[Frontend] Repair Recharts pie-label typings in DataVisualizationDashboard

## Problem

The chart reads a nonexistent region property and assumes percent is always defined, breaking TypeScript compilation.

## Relevant code

`src/components/analytics/DataVisualizationDashboard.tsx`

## Proposed scope

Use the supported PieLabelRenderProps contract, handle optional values, and add a render test covering incomplete chart 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 with src/components/analytics/DataVisualizationDashboard.tsx and inspect the pie-label rendering against the supported PieLabelRenderProps contract. Add a focused render test for incomplete chart data, then run the related tests and TypeScript checks. Done means optional values are handled without reading the nonexistent region property and the regression coverage passes.

Written by the indexing model from the issue text.