Add optional Apple Books button to downloads and book cards; v1.1.42

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

src/content.ts

@@ -31,6 +31,8 @@ export interface CustomLink {
   description?: string
   amazonUrl?: string
   amazonLabel?: string
+  appleBooksUrl?: string
+  appleBooksLabel?: string
   tags?: string[]
 }
 
@@ -158,6 +160,8 @@ export interface SiteContent {
   studyGuideDownloadUrl: string
   studyGuideUrl: string
   studyGuideAmazonButtonLabel: string
+  studyGuideAppleBooksUrl: string
+  studyGuideAppleBooksLabel: string
   // ── Colossians Study ──
   studies: StudyProgram[]
   colossiansStudySections: ColossiansStudySection[]
@@ -337,6 +341,8 @@ export const DEFAULTS: SiteContent = {
   studyGuideDownloadUrl: '',
   studyGuideUrl: 'https://a.co/d/01sG2tOJ',
   studyGuideAmazonButtonLabel: 'Get it on Amazon',
+  studyGuideAppleBooksUrl: '',
+  studyGuideAppleBooksLabel: 'Get it on Apple Books',
   studies: [
     {
       id: 'study-colossians',