Add study account engagement features; v1.2.4

- Pause reminders: remindersPausedUntil field + scheduler skip + account UI with 7/14/30-day presets
- Email digest mode: reminderFrequency field (immediate/weekly) + weekly digest email + scheduler + account UI toggle
- Admin user list improvements: streak, reengagement, frequency, pause, per-study lesson progress
- Admin manual re-engagement: POST endpoint + tier selector button in admin panel
- Study bookmarks: bookmarkedSectionIds in progress file + POST/DELETE endpoints + toggle button in lesson UI
- Study completion certificate email: auto-sent on first certificate issuance
- Content fields for certificate and weekly digest email templates in admin

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/study-helpers.js

@@ -622,6 +622,9 @@ export async function scheduleStudyReminders(sendStudyReminderEmail) {
 
   for (const user of state.studyUsers) {
     if (user.studyRemindersEnabled !== true) continue
+    if (user.reminderFrequency === 'weekly') continue
+    const pausedUntil = user.remindersPausedUntil ? new Date(user.remindersPausedUntil) : null
+    if (pausedUntil && !isNaN(pausedUntil.getTime()) && pausedUntil > now) continue
     const email = user.username
     const displayName = user.displayName || email
     const enrolledStudySlugs = Array.isArray(user.enrolledStudySlugs) ? user.enrolledStudySlugs : []
@@ -677,7 +680,7 @@ function getReengagementTiers() {
   return days.slice(0, 3).map((d, i) => ({ key: `t${i + 1}`, days: d }))
 }
 
-function makeUnsubUrl(userId) {
+export function makeUnsubUrl(userId) {
   const secret = process.env.RESEND_WEBHOOK_TOKEN ?? 'siteforge'
   const token = createHmac('sha256', secret).update(userId).digest('hex')
   const canonical = state.cachedSiteContent?.seo?.canonicalUrl || 'https://versebyversewithnate.us/'
@@ -694,6 +697,8 @@ export async function scheduleReengagementEmails(sendStudyReengagementEmail) {
   for (const user of state.studyUsers) {
     if (user.studyRemindersEnabled !== true) continue
     if (!user.lastLoginAt) continue
+    const pausedUntil = user.remindersPausedUntil ? new Date(user.remindersPausedUntil) : null
+    if (pausedUntil && !isNaN(pausedUntil.getTime()) && pausedUntil > now) continue
     const lastLogin = new Date(user.lastLoginAt)
     if (isNaN(lastLogin.getTime())) continue
     const daysSinceLogin = (nowMs - lastLogin.getTime()) / (1000 * 60 * 60 * 24)
@@ -733,3 +738,77 @@ export async function scheduleReengagementEmails(sendStudyReengagementEmail) {
     }
   }
 }
+
+// ── Weekly digest scheduler ───────────────────────────────────────────────
+
+export async function scheduleWeeklyDigestEmails(sendStudyWeeklyDigestEmail) {
+  if (!state.cachedSiteContent) return
+  const now = new Date()
+  const nowMs = now.getTime()
+  const ONE_WEEK_MS = 7 * 24 * 60 * 60 * 1000
+
+  for (const user of state.studyUsers) {
+    if (user.reminderFrequency !== 'weekly') continue
+    if (user.studyRemindersEnabled !== true) continue
+
+    const pausedUntil = user.remindersPausedUntil ? new Date(user.remindersPausedUntil) : null
+    if (pausedUntil && !isNaN(pausedUntil.getTime()) && pausedUntil > now) continue
+
+    const lastDigestMs = user.weeklyDigestSentAt ? new Date(user.weeklyDigestSentAt).getTime() : 0
+    if (nowMs - lastDigestMs < ONE_WEEK_MS) continue
+
+    const enrolledStudySlugs = Array.isArray(user.enrolledStudySlugs) ? user.enrolledStudySlugs : []
+    if (enrolledStudySlugs.length === 0) continue
+
+    const userSent = state.studyReminders.users[user.id] ?? {}
+    const lessons = []
+    const newlySentByStudy = {}
+
+    for (const studySlug of enrolledStudySlugs) {
+      const study = Array.isArray(state.cachedSiteContent.studies)
+        ? state.cachedSiteContent.studies.find(item => normalizeStudySlug(item?.slug) === studySlug)
+        : undefined
+      if (!study) continue
+
+      for (const section of study.sections ?? []) {
+        const releaseTime = getSectionReleaseTime(section)
+        if (!Number.isFinite(releaseTime) || releaseTime > nowMs) continue
+        const sentForStudy = Array.isArray(userSent[studySlug]) ? userSent[studySlug] : []
+        if (sentForStudy.includes(section.id)) continue
+
+        const canonical = state.cachedSiteContent?.seo?.canonicalUrl || 'https://versebyversewithnate.us/'
+        const base = canonical.endsWith('/') ? canonical.slice(0, -1) : canonical
+        lessons.push({
+          sectionId: section.id,
+          studySlug,
+          sectionTitle: section.title ?? section.id,
+          sectionReference: section.reference ?? '',
+          studyTitle: study.title ?? studySlug,
+          sectionUrl: `${base}/study/${study.slug}/${section.id}`,
+        })
+        if (!newlySentByStudy[studySlug]) newlySentByStudy[studySlug] = []
+        newlySentByStudy[studySlug].push(section.id)
+      }
+    }
+
+    if (lessons.length === 0) continue
+
+    const unsubUrl = makeUnsubUrl(user.id)
+    try {
+      await sendStudyWeeklyDigestEmail(user.username, user.displayName || user.username, lessons, unsubUrl)
+    } catch (err) {
+      console.error(`[study-digest] failed to send digest to ${user.username}:`, err)
+      continue
+    }
+
+    for (const [studySlug, sectionIds] of Object.entries(newlySentByStudy)) {
+      const sentForStudy = Array.isArray(userSent[studySlug]) ? userSent[studySlug] : []
+      userSent[studySlug] = [...new Set([...sentForStudy, ...sectionIds])]
+    }
+    state.studyReminders.users[user.id] = userSent
+    queueStudyRemindersWrite()
+
+    user.weeklyDigestSentAt = now.toISOString()
+    queueStudyUsersWrite()
+  }
+}