delete sampleArticles seed; serve all sections from bb.wp_imported_posts (DB)

Eliminates 72 hardcoded rocket.new image refs in one shot. Section pages
(/gear, /technology, /show-coverage, /news) now render from
bb.wp_imported_posts via getLegacyArticlesBySection(section), which maps
each non-news section to a curated tag set (e.g. gear -> Audio, Cameras,
lighting, Blackmagic Design, monitoring; technology -> AI, Streaming,
OTT, IP, Cloud, AV; show-coverage -> NAB, IBC, BroadcastAsia).

Also:
- src/lib/articles/types.ts: Article interface lifted out of the deleted
  seed file. Type-only consumers (NewsArticleDetailClient,
  ArticleDetailClient, legacy-source) re-imported from here.
- /news (client component) now wrapped: server fetches articles from DB
  and passes to NewsPageClient. Filter UI unchanged.
- generateStaticParams on /news/[slug] and /articles/[slug] no longer
  references seed slugs; pre-renders 50 most-recent imported slugs and
  relies on dynamicParams + revalidate=3600 for the rest.
- sitemap.ts now sources article URLs from
  getLegacyRecentSitemapEntries() (up to 5000 most-recent imported posts).
  Default BASE_URL fallback updated from the rocket.new placeholder to
  bb-staging.onsethost.com.
- src/app/api/ai/article-suggestions/route.ts now pulls candidates from
  the DB (top 100 recent news) and resolves AI-returned slugs via DB
  lookup if not in the candidate window.

Inline rocket.new image refs in homepage components (ArticleFeed,
FeaturedBento) are unchanged in this commit; those are inline seed
arrays in the components, not imports of sampleArticles.

src/app/news/[slug]/NewsArticleDetailClient.tsx

@@ -6,7 +6,7 @@ import Header from "@/components/Header";
 import Footer from "@/components/Footer";
 import AdSlot from "@/components/AdSlot";
 import { createClient } from "@/lib/supabase/client";
-import type { Article } from "@/lib/articles/sampleArticles";
+import type { Article } from "@/lib/articles/types";
 
 interface NewsArticleDetailClientProps {
   article: Article;