feat: homepage newsletter, Q&A callout, episodes page redesign, SEO/sitemap, asset tagging

- Fix "Invalid Date" on student account page (memberSince guard)
- Fix study community author showing full email instead of username
- Add newsletter sign-up section to homepage (between PRISM and Current Series)
- Add newsletter opt-in nudge to study enrollment flow
- Redesign episodes page: latest episode featured card + per-episode Spotify embed
- Add SEO description field to episodes page (visually hidden, admin-editable)
- Expand default sitemap paths to include /about, /contact, /episodes, /resources, /study, /study/titus, /study/colossians
- Add featured Q&A callout section to homepage
- Add Q&A callout to study hub footer
- Tag both untagged image assets in Asset Manager

server/helpers.js

@@ -29,7 +29,7 @@ export const DEFAULT_SEO = {
   ogImage: '/images/podcast-art.jpeg',
   canonicalUrl: 'https://versebyversewithnate.us/',
   robotsPolicy: 'index,follow',
-  sitemapPaths: ['/', '/start-here', '/questions', '/privacy', '/terms'],
+  sitemapPaths: ['/', '/start-here', '/questions', '/privacy', '/terms', '/about', '/contact', '/episodes', '/resources', '/study', '/study/titus', '/study/colossians'],
 }
 
 export const DEFAULT_LEGAL = {
@@ -338,6 +338,7 @@ export function sanitizeSiteContent(siteContent) {
     colossiansStudySections: sanitizeColossiansStudySections(siteContent.colossiansStudySections),
     redirects: sanitizeRedirectRules(siteContent.redirects),
     podcastFeaturedLinks: sanitizeFeaturedLinks(siteContent.podcastFeaturedLinks ?? DEFAULT_PODCAST_FEATURED_LINKS),
+    episodesSeoIntro: typeof siteContent.episodesSeoIntro === 'string' && siteContent.episodesSeoIntro.trim() ? siteContent.episodesSeoIntro.trim().slice(0, 600) : '',
     seo: {
       title: typeof seo.title === 'string' && seo.title.trim() ? seo.title.trim().slice(0, 120) : DEFAULT_SEO.title,
       description: typeof seo.description === 'string' && seo.description.trim() ? seo.description.trim().slice(0, 240) : DEFAULT_SEO.description,