[#13365] Add validation for email input in feedback form

[Shuhui-Yang525]

Fixes #13365 Implemented client-side validation for email-type questions in feedback sessions. Now, when a question in a feedback session expects an email address, the input field validates the format before submission. Users will only be able to submit the form if the entered value is a valid email.

Additionally:

Added corresponding error message styling: invalid email inputs are highlighted in red.

Updated relevant CSS classes to ensure error state is clear and consistent with the existing UI styling.

Tested to confirm correct behavior:

Valid email format → form submits normally.

Screenshots are included below to demonstrate the UI changes Before:

After:

[github-actions[bot]]

Hi @Shuhui-Yang525, thank you for your interest in contributing to TEAMMATES! However, your PR does not appear to follow our contribution guidelines:

• Description must reference the issue number the PR is fixing, e.g. Fixes #<issue-number> (or Part of #<issue-number> if the PR does not address the issue fully)

Please address the above before we proceed to review your PR.

[Qilin127]

I'm a group member and I tested this function.

[Mees1ks]

Good work but needs minor adjustments for consistency.