feat(events): event host applications — applicant submission UI

Give prospective event hosts a place to apply and track their applications.

Scope

An "Apply to host" area reachable by any logged-in user.
A list of currently-open intakes (program · season · level); if none are open, applying is disabled with an explanation.
A proposal form that renders from the selected intake's configuration — showing and requiring only the fields the admin enabled — including the additional-helper invite list (email + role) and the optional reimbursement/how-to-pay section, with required-field validation.
A "re-apply from last year" option that prefills from a prior application or a prior event the user hosted.
A list of the user's own applications with status, and the ability to edit and resubmit when changes are requested.
A timeline showing reviewer comments on returned or rejected applications.

The apply area is reachable by any logged-in user; when no intake is open, applying is clearly disabled.
The form shows exactly the fields the chosen intake enabled, enforces its required fields, and supports the additional-role list and payout section.
A user can create, edit (while Draft / Changes Requested), submit, and resubmit an application.
A user can re-apply with data prefilled from a prior application or hosted event, then edit it.
A user can see each application's status and read reviewer comments.
Success / error feedback uses the standard in-app notification pattern, and layout matches existing screens.

Part of the Event Host Applications feature for v26.4.