[TechTix]: Update Miscellaneous Step

[seangaaab]

Figma / Design Link

https://www.figma.com/design/7T8qFvssYvyM2M5gI2FoXi/PyCon-2026?node-id=104-2&p=f&t=5Kq6JgpowVBgjAUi-0

Description / Objective

• To update Miscellaneous step UI to match this year's design
• Copy existing form handling and ensure that form still works as expected.
• Only styles/structure should be updated.
• TechTix –frontend/src/pages/client/pycon/register/steps/MiscellaneousStep.tsx

Responsive Design Requirements

• Mobile (Small screens, <768px)
• Tablet (Medium screens, >=768px)
• Desktop (Large screens, >=1024px)

Acceptance Criteria

• The UI implementation matches the figma design
• "Are you a member..." and "Would you like to volunteer..." form fields should still default to No
• Both Dietary Restrictions and Accessibility Needs should be optional fields
• The name prop of each <FormItem /> should still be the same. No changes. If there are any questions regarding the mapping of the names to the design, please ask @seangaaab
• Clicking the "Next" button should trigger form errors if there are empty/invalid form values. If there are no form errors, the "Next" button should navigate the user to the next step