Add admin control for hero podcast art image; v1.1.28

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

src/content.ts

@@ -101,6 +101,7 @@ export interface LegalSettings {
 
 export interface SiteContent {
   // ── Hero ──
+  podcastArtUrl: string
   eyebrow: string
   heroTagline: string
   heroBtnSpotify: string
@@ -275,6 +276,7 @@ export interface SiteContent {
 }
 
 export const DEFAULTS: SiteContent = {
+  podcastArtUrl: '/images/podcast-art.jpeg',
   eyebrow: 'A Journey Through Scripture',
   heroTagline: "Exploring God's Word one verse at a time",
   heroBtnSpotify: 'Listen on Spotify',