Add structured show notes form to Episode Highlights; v1.2.3

Replace single showNotes textarea with five guided fields: Episode Summary,
Key Themes, Scripture References, Key Quotes, and Resources & Links. Legacy
showNotes content is preserved as a backward-compatible fallback — it
auto-populates the Summary field in the admin editor and renders on the public
episode detail page until overwritten with structured data.

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

src/content.ts

@@ -67,6 +67,13 @@ export interface PodcastFeaturedLink {
   summary: string
   url: string
   embedUrl?: string
+  // Structured show notes fields
+  showNotesSummary?: string
+  showNotesThemes?: string[]
+  showNotesScripture?: string[]
+  showNotesQuotes?: string[]
+  showNotesResources?: string[]
+  // Legacy plain-text field — kept for backward compat with live data
   showNotes?: string
   discussionQuestions?: string[]
 }