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/show-coverage/page.tsx

@@ -4,7 +4,9 @@ import Link from "next/link";
 import Header from "@/components/Header";
 import Footer from "@/components/Footer";
 import AppImage from "@/components/ui/AppImage";
-import { getArticlesBySection } from "@/lib/articles/sampleArticles";
+import { getLegacyArticlesBySection } from "@/lib/articles/legacy-source";
+
+export const revalidate = 1800;
 
 export const metadata: Metadata = {
   title: "NAB Show, IBC & Broadcast Event Coverage — BroadcastBeat",
@@ -20,8 +22,8 @@ export const metadata: Metadata = {
   },
 };
 
-export default function ShowCoveragePage() {
-  const articles = getArticlesBySection("show-coverage");
+export default async function ShowCoveragePage() {
+  const articles = await getLegacyArticlesBySection("show-coverage");
   const nabArticles = articles.filter((a) => a.tags.includes("NAB 2026"));
 
   return (