One companion study guide per series; v2.9.8

- Second series gets its own guide (Resources page card, download page, admin fields)
- When a series ends (scheduled or manual) its guide moves onto its Finished Book, which shows a guide button; the main series' guide is cleared unless the launch supplies a new one
- Lane B launch schedule can supply the incoming series' guide
- Download lookup covers second-series and finished-book guides; guide URLs are sanitized on save and on use

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

server/helpers.js

@@ -297,6 +297,22 @@ function sanitizeIsoDate(value) {
   return Number.isFinite(time) ? new Date(time).toISOString() : ''
 }
 
+function sanitizeStudyGuide(value) {
+  if (!value || typeof value !== 'object' || Array.isArray(value)) return undefined
+  const str = (v, max) => (typeof v === 'string' ? v.trim().slice(0, max) : '')
+  const title = str(value.title, 140)
+  if (!title) return undefined
+  return {
+    title,
+    description: str(value.description, 4000),
+    downloadUrl: sanitizeUrl(value.downloadUrl),
+    amazonUrl: sanitizeUrl(value.amazonUrl),
+    amazonLabel: str(value.amazonLabel, 80),
+    appleBooksUrl: sanitizeUrl(value.appleBooksUrl),
+    appleBooksLabel: str(value.appleBooksLabel, 80),
+  }
+}
+
 function sanitizeSecondSeries(value) {
   if (!value || typeof value !== 'object' || Array.isArray(value)) return undefined
   const str = (v, max) => (typeof v === 'string' ? v.trim().slice(0, max) : '')
@@ -310,6 +326,7 @@ function sanitizeSecondSeries(value) {
     listenBtnLabel: str(value.listenBtnLabel, 80),
     studySlug: str(value.studySlug, 120).toLowerCase().replace(/[^a-z0-9-]/g, '-'),
     ...(season ? { season } : {}),
+    ...(sanitizeStudyGuide(value.guide) ? { guide: sanitizeStudyGuide(value.guide) } : {}),
   }
 }
 
@@ -410,6 +427,9 @@ export function sanitizeSiteContent(siteContent) {
     archivedSeries: sanitizeArchivedSeries(siteContent.archivedSeries),
     studies: sanitizeStudies(siteContent.studies),
     secondSeries: sanitizeSecondSeries(siteContent.secondSeries),
+    finishedBooks: Array.isArray(siteContent.finishedBooks)
+      ? siteContent.finishedBooks.map(book => (book && typeof book === 'object' ? { ...book, guide: sanitizeStudyGuide(book.guide) } : book))
+      : siteContent.finishedBooks,
     colossiansStudySections: sanitizeColossiansStudySections(siteContent.colossiansStudySections),
     redirects: sanitizeRedirectRules(siteContent.redirects),
     podcastFeaturedLinks: sanitizeFeaturedLinks(siteContent.podcastFeaturedLinks ?? DEFAULT_PODCAST_FEATURED_LINKS),