Hide Enroll for planned studies (Coming soon) and reject planned enrollments server-side; v2.8.3

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/routes/study-data.js

@@ -59,6 +59,11 @@ export function register(app) {
 
     const enrolled = Array.isArray(user.enrolledStudySlugs) ? user.enrolledStudySlugs : []
     if (!enrolled.includes(studySlug)) {
+      const catalogEntry = getStudyCatalog().find(study => study.slug === studySlug)
+      if (catalogEntry?.status === 'planned') {
+        res.status(400).json({ message: 'This study is not open for enrollment yet.' })
+        return
+      }
       user.enrolledStudySlugs = [...enrolled, studySlug].slice(0, MAX_STUDY_ENROLLMENTS_PER_USER)
       user.updatedAt = new Date().toISOString()
       queueStudyUsersWrite()