Fix Join Us (Events Page) Bugs

[unix2dossss]

• [x] Fix Validation Bugs: Final 'submit' button doesn't validate properly.
• [x] Implement Submit backend
• [ ] Improve UI: Overall. + Update Contact information section.-

Stupid Bugs

• [x] Student ID should be 9 digits in length. (I made it 10 🥲)

[unix2dossss]

Mantine Container seems to have a really large padding. Potentially can fix X-scrolling.

[unix2dossss]

Added Paid Col. Set to False by default.