Date of Birth accepts unrealistic values (e.g. 01/01/1400 or 01/01/3000)

[iamtanuj18]

The Date of Birth field on the participant registration form has no bounds. Tested with 01/01/1400 (over 600 years ago) and 01/01/3000 (nearly 1000 years in the future) - both submit fine and render on the personal details page as-is.

nice to have sanity bounds:

• Reject future dates outright
• Reject dates more than ~120 years ago (unlikely to be a valid DoB)

Fix: add min/max attributes on the DoB input in application/user-client/src/pages/Register.tsx for client-side feedback, plus matching range validation on the backend in registerParticipant since there isn't one currently.