av: clone broadcastbeat sources + AV Beat rebrand (Phase 1)

- Replaces the prior Rocket scaffold (saved on pre-bb-clone-rollback branch)
- Domain: broadcastbeat.com -> avbeat.com
- Brand: Broadcast Beat -> AV Beat
- Slug: broadcastbeat -> avbeat (package, identifiers)
- Schema fallback: bb -> av (env var name unchanged)
- Placeholder AV BEAT logo (gold->red gradient) at /assets/logos/av.svg
- All BB/RMP logo references repointed

Outstanding before public DNS swap:
  - Supabase av schema bootstrap (mirror of bb tables)
  - WordPress archive import (avbeat-com -> av.articles)
  - Coolify env vars
  - dev-avbeat.onsethost.com staging deploy + visual review

supabase/functions/send-article-notification/index.ts

@@ -34,7 +34,7 @@ serve(async (req) => {
       throw new Error("RESEND_API_KEY is not set");
     }
 
-    const siteUrl = "https://broadcastbeat.com";
+    const siteUrl = "https://avbeat.com";
     const articleUrl = article.slug
       ? `${siteUrl}/articles/${article.slug}`
       : article.wp_slug