Improve pre-deployment validation and UX guardrails

[beanbean9339]

Strengthen validation to reduce invalid metadata exports before deployment.

Tasks

• Enforce required field validation more strictly
• Validate publication date format (YYYY-MM-DD)
• Validate ORCID format consistently
• Improve inline error display instead of only alerts

Acceptance criteria

• Invalid inputs are clearly flagged in UI
• Users cannot export malformed metadata
• Validation is consistent across CITATION.cff and Zenodo outputs