homepage: remove top bar + fix subscribe + Staff Editorial header

1. Remove SystemStatusBar from root layout. The "29,220 articles
   indexed / 13 events tracked / [v2.0.0]" strip ate vertical space
   above the fold without serving readers.

2. /api/newsletter/subscribe was returning 500 "Failed to save
   subscription" because:
   - The route used the anon-session client and tried to UPSERT on
     bb.newsletter_subscribers, but the table's RLS only has an
     INSERT policy for the public role. Upsert needs INSERT+UPDATE,
     so the second branch failed RLS.
   - Switched to createAdminClient (service-role) — bypasses RLS,
     which is fine because this is a server-side endpoint with
     server-side email validation.
   - Welcome email now sends via nodemailer in a non-blocking
     background task so a slow SMTP doesn't hold up the response.
     Newer HTML template, brand-aligned, with a real CTA back to
     /news.

   Side work to wire SMTP (done out-of-band):
   - Created newsletter@broadcastbeat.com mailbox in Mailcow via
     the API (2GB quota, active, no force-pw-update).
   - Set SMTP_HOST=mail.onsethost.com, SMTP_PORT=587,
     SMTP_USER/PASS/FROM_EMAIL/FROM_NAME in Coolify env so the
     welcome email actually fires after the next deploy.

3. FeaturedBentoFromDb section header: "Featured · staff editorial"
   (small mono caps) → "Staff Editorial" (font-serif 2xl/3xl, bold,
   with a thin metadata line "Selected by our newsroom" beside it
   and a 2px bottom rule). Matches the editorial typography on the
   article pages.

src/app/layout.tsx

@@ -1,7 +1,8 @@
 import React, { Suspense } from 'react';
 import type { Metadata, Viewport } from 'next';
 import '../styles/tailwind.css';
-import SystemStatusBar from '@/components/SystemStatusBar';
+// SystemStatusBar removed — the "articles indexed / events tracked / [v2.0.0]"
+// strip was eating vertical space without serving readers.
 import AskBBAI from '@/components/AskBBAI';
 import GoogleAnalytics from '@/components/GoogleAnalytics';
 import CookieConsent from '@/components/CookieConsent';
@@ -131,7 +132,6 @@ export default function RootLayout({
         <Suspense fallback={null}>
           <GoogleAnalytics />
         </Suspense>
-        <SystemStatusBar />
         <div className="page-transition" id="main-content">
           {children}
         </div>