chore(deps): update UI runtime dependencies (#1573)

## Description

Update Preact, Signals, Marked, and Radix UI packages within their current majors. Align Vitest dependency inlining with the updated Radix transitive modules.

Closes codemem-jnd6.5.

## Type of Change

- [ ] 🚀 Feature (new functionality)
- [ ] 🐛 Bug fix (fixes an issue)
- [ ] 📚 Documentation (docs-only change)
- [x] 🔧 Maintenance (refactor, chore, CI, etc.)
- [ ] 🧪 Testing (test-only changes)

## Testing

- [x] Relevant checks pass locally (`pnpm run tsc`, `pnpm run lint`, `pnpm run test`)
- [ ] Added/updated tests for changes
- [x] Manually verified changes work as expected

Additional checks: UI typecheck, 948 UI tests, UI production build, Snyk high-severity SCA scan.

## Checklist

- [x] Code follows project style (`pnpm run lint` passes for touched files)
- [x] Self-review completed
- [x] Documentation updated (not needed)
- [x] No new warnings introduced