Add email reminders to calendar episodes; v1.1.15

- Per-episode reminder select (1d/2d/3d/1wk/2wk before publish date)
- Server checks hourly; fires Resend email to admin on reminder day
- reminderSentAt persisted so reminders don't re-fire; cleared if date or setting changes
- Bell indicator on calendar chips; sent confirmation in edit popover

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

server.js

@@ -50,6 +50,7 @@ import { register as registerStudyComments } from './server/routes/study-comment
 import { register as registerStudyCertificate } from './server/routes/study-certificate.js'
 import { register as registerEpisodeScripts } from './server/routes/episode-scripts.js'
 import { register as registerContact } from './server/routes/contact.js'
+import { startReminderScheduler } from './server/reminder.js'
 import { register as registerInboundEmail } from './server/routes/inbound-email.js'
 import { register as registerQuestions } from './server/routes/questions.js'
 import { register as registerAnalytics } from './server/routes/analytics.js'
@@ -156,6 +157,8 @@ Promise.all([
       createBackupSnapshot('scheduled').catch(() => {})
     }, BACKUP_INTERVAL_MS)
 
+    startReminderScheduler()
+
     // Purge expired study sessions every hour
     setInterval(() => {
       const now = Date.now()