Aggiunge registry nodi stream e provisioning Hetzner/lab per lo scale-out.

Prepara l'architettura multi-nodo (MediaMTX+ffmpeg) con assignment URL per sessione, admin di provision/drain e provider Cloud/DNS astratti verso mltv-stream.net.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/services/recordings/cleanup_local.rb

@@ -95,7 +95,7 @@ module Recordings
     def cleanup_mediamtx_path(session)
       return unless session.status.in?(%w[ended error])
 
-      Mediamtx::Client.new.delete_path(session)
+      Mediamtx::Client.for_session(session).delete_path(session)
     rescue Mediamtx::Client::Error => e
       @logger.warn("[Recordings::CleanupLocal] delete_path #{session.id}: #{e.message}")
     end