Enhance exhibitor submission UX with loading feedback and status visibility

[sandy191020]

Fixes #

Overview

This PR improves the exhibitor submission workflow by enhancing user feedback and status visibility.

Changes Made

UI/UX Improvements

• Added loading indicator during form submission
• Disabled submit button to prevent duplicate submissions
• Displayed success confirmation message after submission
• Added "Pending Approval" status badge in exhibitor UI

Backend Enhancement

• Introduced a persistent status field for exhibitors
• Default status set to "Pending Approval"
• Enables consistent state across reloads and API usage

Error Handling

• Improved user-friendly error messages for failed submissions
• Prevented raw error outputs in UI

User Experience

After these changes:

• Users see a loading spinner while submitting
• Duplicate submissions are prevented
• Clear success feedback is shown
• Submitted exhibitors display a "Pending Approval" status

Notes

• While the original issue focused on UI feedback, a minimal backend enhancement was added to persist the status and improve consistency.
• I’m happy to refine or scope this further based on maintainer feedback.

Testing

• Verified functionality through manual testing
• Added basic test assertion for default "pending" status
• Full test suite could not be executed due to local environment limitations

Impact

This improves clarity, prevents user confusion, and enhances the overall exhibitor submission experience.

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[sandy191020]

Fixes #28