[Frontend] Redact credentials and health data from debug utilities

## Problem

The broad debug snapshot and history system can accidentally retain tokens, wallet data, contact details, or medical content.

## Relevant code

`src/utils/debug.ts`

## Proposed scope

Introduce recursive redaction, field allowlists, retention limits, and tests with nested sensitive payloads.

## 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/utils/debug.ts and reproduce or characterize the reported retention behavior in a focused automated test using nested sensitive payloads. Define coverage for recursive redaction, field allowlists, retention limits, empty/loading and failure boundaries where applicable, and verify related tests plus lint and TypeScript checks. Done means credentials and health data are not retained while existing debug behavior and privacy safeguards remain intact.

Written by the indexing model from the issue text.