Improve SMTP host and port validation with descriptor checks and unit…

[wisekiran]

Summary

This PR improves validation for SMTP host and port fields in the MailAccount descriptor.

Changes include:

• Added backend validation to ensure SMTP port is numeric and within the valid range (1–65535)
• Added basic validation to prevent invalid SMTP host values (e.g., containing spaces)
• Added unit tests to verify validation behavior

This change improves configuration UX and adds defensive validation without altering existing email sending behavior.

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Testing done

Automated testing

• Added unit tests covering:
  • Non-numeric SMTP port
  • Out-of-range SMTP port
  • Valid SMTP port
  • Invalid SMTP host containing spaces
  • Valid SMTP host
• Verified mvn clean install completes successfully.

Manual testing

• Ran Jenkins locally using mvn hpi:run
• Verified validation messages appear correctly in the UI
• Confirmed valid values save successfully
• Confirmed existing email sending behavior remains unchanged

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UI Before

UI After

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Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira (no existing issue; UX improvement)
• Link to relevant pull requests
• Ensure you have provided tests that demonstrate the feature works