Add Finished Books feature with episode playlists

- New FinishedBook type in content.ts + finishedBooks[] field on SiteContent
- RSS parser now extracts itunes:season into each episode object
- /finished grid page and /finished/:id playlist page (filters episodes by season)
- Episodes nav link replaced with dropdown: Current Series / Finished Books
- Finished Books link added to footer
- Admin: "End Current Series & Start New Book" wizard on Current Series tab
- Admin: Finished Books management tab (add/edit/remove entries)

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

src/content.ts

@@ -47,35 +47,6 @@ export interface WhereToNextCard {
   path: string
 }
 
-export interface ArchivedSeriesResourceLink {
-  id: string
-  label: string
-  description?: string
-  url: string
-  amazonUrl?: string
-  amazonLabel?: string
-}
-
-export interface ArchivedSeriesNote {
-  id: string
-  heading: string
-  body: string
-}
-
-export interface ArchivedSeries {
-  id: string
-  label: string
-  title: string
-  description: string
-  imageUrl: string
-  listenUrl: string
-  studyGuideTitle: string
-  studyGuideDescription: string
-  studyGuideUrl: string
-  resourceLinks: ArchivedSeriesResourceLink[]
-  notes: ArchivedSeriesNote[]
-  episodeRange?: { from: number; to: number }
-}
 
 export interface RedirectRule {
   id: string
@@ -95,6 +66,14 @@ export interface PodcastFeaturedLink {
   discussionQuestions?: string[]
 }
 
+export interface FinishedBook {
+  id: string
+  title: string
+  description: string
+  imageUrl: string
+  season: number
+}
+
 export interface SeoSettings {
   title: string
   description: string
@@ -260,13 +239,14 @@ export interface SiteContent {
   // ── Arrays ──
   customLinks: CustomLink[]
   customBlocks: CustomBlock[]
-  archivedSeries: ArchivedSeries[]
   redirects: RedirectRule[]
   podcastFeaturedLinks: PodcastFeaturedLink[]
   seo: SeoSettings
   legal: LegalSettings
   // ── Episodes page ──
   episodesSeoIntro: string
+  // ── Finished Books ──
+  finishedBooks: FinishedBook[]
 }
 
 export const DEFAULTS: SiteContent = {
@@ -445,7 +425,6 @@ export const DEFAULTS: SiteContent = {
   cookieBannerText: 'We use optional analytics cookies to better understand how people find and engage with this content. By accepting, you allow us to measure how you interact with the site — no personal data is sold or shared.',
   customLinks: [],
   customBlocks: [],
-  archivedSeries: [],
   redirects: [
     {
       id: 'spotify',
@@ -467,6 +446,7 @@ export const DEFAULTS: SiteContent = {
     },
   ],
   podcastFeaturedLinks: [],
+  finishedBooks: [],
   episodesSeoIntro: 'Verse by Verse with Nate is an expository Bible teaching podcast where we go through Scripture one verse at a time. Each episode digs into the text carefully and practically, helping you understand what the Bible says, what it means, and how to live it out. New episodes released regularly — subscribe on Spotify or your favorite podcast platform.',
   seo: {
     title: 'Verse by Verse with Nate',