fix: Update dependencies to resolve Dependabot security alerts

Security updates:
- happy-dom: 17.4.1 → 20.0.10 (fixes 2 CRITICAL alerts)
- @playwright/test: 1.51.0 → 1.56.1 (fixes 1 HIGH alert)
- vite: 6.3.6 → 7.2.2 (fixes 1 MEDIUM alert, via vitest)
- parcel: 2.12.0 → 2.16.1 (fixes 2 MEDIUM alerts)
- js-yaml: removed from dependency tree (resolved by parcel update)
- vitest: 3.0.8 → 3.2.4 (pulls in updated vite)

All unit tests passing (233 tests).
TypeScript build successful.

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Co-Authored-By: Claude <[email protected]>

Author: idvorkin