Add scheduled series auto-launch for series card, Start Here, and study guide; v2.0.36

One scheduled date/time in the Current Series admin panel archives the active series to
Finished Books and atomically swaps in new content for the series card, Start Here steps,
and Companion Study Guide. Server checks every hour via setInterval; also runs on restart
so the transition fires even if the server was down at the scheduled moment.

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

src/content.ts

@@ -320,6 +320,37 @@ export interface SiteContent {
   episodesSeoIntro: string
   // ── Finished Books ──
   finishedBooks: FinishedBook[]
+  // ── Scheduled Series Transition ──
+  // All fields fire together at triggersAt. Start Here and Study Guide fields are optional —
+  // omit them to leave those sections unchanged when the series transitions.
+  scheduledSeriesTransition?: {
+    triggersAt: string   // ISO datetime — server fires at or after this time (checks hourly)
+    // New series card
+    newTitle: string
+    newDescription?: string
+    newImageUrl?: string
+    newSeason: number
+    // Start Here section (optional)
+    newStartHereHeading?: string
+    newStartHereIntro?: string
+    newStartHereStep1Title?: string
+    newStartHereStep1Body?: string
+    newStartHereStep1Cta?: string
+    newStartHereStep2Title?: string
+    newStartHereStep2Body?: string
+    newStartHereStep2Cta?: string
+    newStartHereStep3Title?: string
+    newStartHereStep3Body?: string
+    newStartHereStep3Cta?: string
+    // Companion Study Guide / Featured Download (optional)
+    newStudyGuideTitle?: string
+    newStudyGuideDescription?: string
+    newStudyGuideDownloadUrl?: string
+    newStudyGuideUrl?: string
+    newStudyGuideAmazonButtonLabel?: string
+    newStudyGuideAppleBooksUrl?: string
+    newStudyGuideAppleBooksLabel?: string
+  }
   // ── Testimonials ──
   testimonials: Testimonial[]
   // ── Nuggets (sub-show) ──