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

src/app/api/ai/fetch-url/route.ts

@@ -38,7 +38,7 @@ export async function POST(request: NextRequest) {
     try {
       response = await fetch(url, {
         headers: {
-          'User-Agent': 'Mozilla/5.0 (compatible; Broadcast Beat/1.0; +https://broadcastbeat.com)',
+          'User-Agent': 'Mozilla/5.0 (compatible; AV Beat/1.0; +https://avbeat.com)',
           'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
         },
         signal: controller.signal,