[Frontend] — Event branding: category & banner on cards, header, and listing filter

[Olowodarey]

Background

Neither EventCard nor EventHeader know about category/bannerUrl
(both added to CreatorEvent in Issue 1):

The listing page ((authenticated)/creator-events/page.tsx) has status
filter buttons (lines 78-90) but no category filter, and its local
CreatorEvent interface (lines 9-21, a page-local duplicate of the
context's type — note this duplication, but resolving it is out of scope
here) also lacks category/bannerUrl.

Goal

Surface category (as a badge) and bannerUrl (as a card/header banner
image, with a graceful fallback) on EventCard and EventHeader, and add a
category filter to the listing page.

Acceptance Criteria

• EventCard shows a category badge for every event, and a banner image
• EventHeader shows the same category badge and an optional full-width
• The listing page has a category filter row; selecting a category
• An <img> with a broken/unreachable bannerUrl doesn't show a broken-