fix(home): restore homepage event banner styling

The .event-banner rules were dropped during an _event.css rewrite, so the
homepage promo banner rendered unstyled (full-width dark text, no gradient).
Restored the banner styles and removed the em-dash from the banner copy.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

css/pages/_event.css

@@ -6,6 +6,19 @@
      that reuses the Become-a-member (.ms-*) look.
    ========================================================================== */
 
+/* ---- homepage promo banner (time-limited: sits above the partners strip) ---- */
+.event-banner { background: linear-gradient(115deg, #F2762E 0%, #E85D2A 55%, #2D738C 100%); color: #fff; padding: 18px 24px; }
+.event-banner-inner { max-width: 1120px; margin: 0 auto; display: flex; align-items: center; justify-content: space-between; gap: 20px; flex-wrap: wrap; }
+.event-banner-copy { display: flex; flex-direction: column; gap: 6px; }
+.event-banner-tag { display: inline-flex; align-items: center; gap: 8px; font-size: 12px; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; opacity: 0.92; }
+.event-banner-text { margin: 0; font-size: 17px; line-height: 24px; color: #fff; }
+.event-banner-cta.btn { background: #fff; color: #E85D2A; border: none; flex: 0 0 auto; white-space: nowrap; }
+.event-banner-cta.btn:hover { background: #FFF3EC; }
+@media (max-width: 700px) {
+    .event-banner-inner { flex-direction: column; align-items: flex-start; }
+    .event-banner-cta.btn { width: 100%; text-align: center; }
+}
+
 /* ---- guide-style centred header (matches the Student Welcome Guide) ---- */
 .news-article--event .news-article-inner { max-width: 820px; }
 .news-article--event .newshub-eyebrow { display: block; text-align: center; color: #2D738C; }