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/middleware.ts

@@ -29,7 +29,7 @@ const RMP_BASE =
   (process.env.NEXT_PUBLIC_RMP_ADS_API
     || "https://advertising.relevantmediaproperties.com").replace(/\/$/, "");
 
-const PROPERTY = "broadcastbeat";
+const PROPERTY = "avbeat";
 const SLOTS = ["728x90", "300x600", "300x250"] as const;
 type Slot = typeof SLOTS[number];