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>

src/content.ts

@@ -94,6 +94,17 @@ export interface Testimonial {
   source?: string
 }
 
+// A series' companion study guide (the main series' guide lives in the studyGuide* fields)
+export interface StudyGuide {
+  title: string
+  description?: string
+  downloadUrl?: string
+  amazonUrl?: string
+  amazonLabel?: string
+  appleBooksUrl?: string
+  appleBooksLabel?: string
+}
+
 export interface SecondSeries {
   label: string
   title: string
@@ -103,6 +114,7 @@ export interface SecondSeries {
   listenBtnLabel: string
   studySlug?: string
   season?: number
+  guide?: StudyGuide
 }
 
 export interface FinishedBook {
@@ -115,6 +127,8 @@ export interface FinishedBook {
   studySlug?: string
   // Episode highlights that were featured while this series was playing, kept for its page
   highlights?: PodcastFeaturedLink[]
+  // The series' companion study guide, kept so it stays available after the series ends
+  guide?: StudyGuide
   downloadUrl?: string
   downloadQrUrl?: string
 }
@@ -128,6 +142,8 @@ export interface ScheduledSeriesTransition {
   newSeason: number
   // Study that opens (planned → active) when this series launches; the ending series' study becomes Complete
   newStudySlug?: string
+  // Companion guide for the incoming series (second series lane only; the main series uses the newStudyGuide* fields)
+  newGuide?: StudyGuide
   // Start Here section (optional)
   newStartHereHeading?: string
   newStartHereIntro?: string