Aggiunge overlay server-side burn-in e stabilizza diretta live.

Tabellone, badge e brand sono ricodificati nel flusso _air via OverlayRelay;
sync punteggio HTTP, volume condiviso rails/sidekiq, qualità 720p migliorata
e badge CONNECTING in ripresa da pausa.

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

backend/app/services/sessions/create.rb

@@ -36,7 +36,11 @@ module Sessions
       StreamSession.transaction do
         session.save!
         session.create_score_state!
-        Mediamtx::Client.new.create_path(session)
+        mtx = Mediamtx::Client.new
+        mtx.create_path(session)
+        mtx.create_overlay_path(session)
+        start_overlay_relay(session)
+        start_youtube_relay(session)
         log_event(session, "pairing", { created: true, platform: session.platform })
       end
 
@@ -70,6 +74,20 @@ module Sessions
       session.rtmp_url = broadcast[:rtmp_url]
     end
 
+    def start_overlay_relay(session)
+      Streams::OverlayRelay.start(session)
+    rescue Streams::OverlayRelay::Error => e
+      Rails.logger.warn("[Sessions::Create] Overlay relay: #{e.message}")
+    end
+
+    def start_youtube_relay(session)
+      return unless session.platform == "youtube"
+
+      Streams::YoutubeRelay.start(session)
+    rescue Streams::YoutubeRelay::Error => e
+      Rails.logger.warn("[Sessions::Create] YouTube relay: #{e.message}")
+    end
+
     def log_event(session, type, metadata)
       session.stream_events.create!(event_type: type, metadata: metadata, occurred_at: Time.current)
     end