fix(contrast): article-body white-on-white — body/dropcap/h2/h3/blockquote/links to navy + slate, drop prose-invert

Article detail pages (/news/[slug] and /articles/[slug]) inherited a dark-theme
prose color palette via the .bb-article-prose ruleset + Tailwind's
prose-invert utility. With the new light surface, every text element in
the article body rendered near-white on white, while the H1 (fixed in
the prior commit) was already navy. Bringing the body in line:

src/styles/tailwind.css:
  - .bb-article-prose wrapper           #d6d4d0  -> #1e293b !important  (slate-800 for long-form body)
  - .bb-article-prose p:first-of-type   #e8e6e0  -> #1e293b
  - .bb-article-prose first-letter      #f0eee8  -> #0F172A             (drop-cap full navy)
  - .bb-article-prose h2                #f5f3ee  -> #0F172A             (in-body subhead matches the page H1)
  - .bb-article-prose h3                #ece9e2  -> #0F172A
  - .bb-article-prose blockquote        #e8e6e0  -> #1e293b
  - .bb-article-prose a (BASE)          #d6d4d0  -> #1D4ED8             (inline links visibly blue at rest, no longer invisible-until-hover; hover unchanged)

src/app/news/[slug]/NewsArticleDetailClient.tsx
src/app/articles/[slug]/ArticleDetailClient.tsx
  - Drop 'prose-invert' from the wrapper className on both routes so any
    descendant the bb-article-prose rules don't explicitly color (lists,
    strong, em, captions) falls back to Tailwind Typography's default
    light-page slate-700 palette.

src/app/articles/[slug]/ArticleDetailClient.tsx

@@ -356,7 +356,7 @@ export default function ArticleDetailClient({ article, relatedArticles, relatedF
             {/* Article Body */}
             {/* DO NOT OVERRIDE — article body prose styles */}
             <div
-              className="bb-article-prose prose prose-invert max-w-none mb-8"
+              className="bb-article-prose prose max-w-none mb-8"
               dangerouslySetInnerHTML={{ __html: article.content }}
             />