fix(mss-2026 form): hide study plans for parents and "other"

Parents and "other" registrants will not be studying, so the "Your study
plans" section is now hidden for those roles. Gating is driven by the role
<select>; validate()/collect() skip any field inside a hidden container, so
the study fields are neither required nor submitted for those roles. Students
(future/current) are unchanged: the section stays visible and required.

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

css/pages/_event.css

@@ -151,8 +151,9 @@
 .msreg .ms-field { min-width: 0; }
 .msreg .ms-field select, .msreg .ms-field input { max-width: 100%; }
 
-/* "study plans" block (always visible, required) */
+/* "study plans" block (shown for students; hidden for parents / "other") */
 .msreg .ev-plans { margin-top: 24px; border: 1px solid #EAECF0; border-radius: 12px; background: #FBFCFD; padding: 4px 18px 20px; }
+.msreg .ev-plans[hidden] { display: none; }
 .msreg .ev-plans-title { font-size: 16px; font-weight: 700; color: #101828; margin: 16px 0 2px; }
 .msreg .ev-plans-lead { font-size: 13px; color: #98A2B3; margin: 0 0 6px; }
 .msreg .ev-subhead { font-size: 13px; font-weight: 700; color: #98A2B3; text-transform: uppercase; letter-spacing: 0.05em; margin: 20px 0 10px; }