Corregge cloud-init montato, PublisherOnline multi-nodo e E2E locale-aware.

Senza volume stream-node i nodi Hetzner nascevano senza MediaMTX; sync live usa ora Client.for_session e rtmpconns (MediaMTX 1.20).

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

backend/app/services/mediamtx/client.rb

@@ -105,6 +105,16 @@ module Mediamtx
       []
     end
 
+    def list_rtmp_conns
+      response = @conn.get("/v3/rtmpconns/list")
+      return [] unless response.success?
+
+      body = response.body
+      body.is_a?(Hash) ? (body["items"] || []) : []
+    rescue Error, Faraday::Error
+      []
+    end
+
     def online_path_names
       Set.new(list_paths.filter_map { |item| item["name"] if item["online"] })
     end