feat(web/apply): persist application form state in localStorage/sessionStorage

[0x4248]

While filling out the moderator application form, navigating away from the page (e.g., via the browser back button) results in all entered data being lost.

Currently, the form state appears to be held only in memory until submission, with no persistence mechanism.

Current behaviour

• Form data is lost if the page is closed, refreshed, or navigated away from
• No recovery mechanism is available when returning to the form

Proposed behaviour

• Persist form state periodically (e.g., via localStorage or sessionStorage)
• Restore previously entered data if the user returns to the form before submission
• Storage is cleared on application submission

blix :3