Fix race create sessione su CPX: ready solo dopo MediaMTX.

I nodi cloud restano in provisioning finché :9997 risponde; retry su create_path e 503 retryable se l’ingest è ancora irraggiungibile.

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

backend/app/controllers/api/v1/base_controller.rb

@@ -2,6 +2,7 @@ module Api
   module V1
     class BaseController < ApplicationController
       rescue_from Teams::EntitlementError, with: :render_entitlement_error
+      rescue_from Streams::IngestUnavailableError, with: :render_ingest_unavailable
       rescue_from BrandingAttachments::CoverUploadError, with: :render_cover_upload_error
       rescue_from Youtube::BroadcastService::Error, with: :render_youtube_error
 
@@ -22,6 +23,13 @@ module Api
         }, status: :forbidden
       end
 
+      def render_ingest_unavailable(error)
+        render json: {
+          error: error.message,
+          error_code: error.code
+        }, status: :service_unavailable
+      end
+
       def render_cover_upload_error(error)
         render json: { error: error.message, error_code: "cover_upload_invalid" }, status: :unprocessable_entity
       end