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/streams/dns_providers/lab.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+module Streams
+  module DnsProviders
+    # DNS lab in Redis (e dump hosts). Nessuna chiamata al registrar.
+    class Lab < Base
+      REDIS_KEY = "stream_dns:a_records"
+
+      def initialize(redis: nil)
+        @redis = redis
+      end
+
+      def upsert_a(name, ip)
+        host = normalize(name)
+        redis.hset(REDIS_KEY, host, ip.to_s)
+        true
+      end
+
+      def delete_a(name)
+        redis.hdel(REDIS_KEY, normalize(name))
+        true
+      end
+
+      def resolve(name)
+        redis.hget(REDIS_KEY, normalize(name))
+      end
+
+      def all_records
+        redis.hgetall(REDIS_KEY)
+      end
+
+      def hosts_file_snippet
+        all_records.sort.map { |host, ip| "#{ip}\t#{host}" }.join("\n")
+      end
+
+      private
+
+      def normalize(name)
+        name.to_s.strip.downcase.delete_suffix(".")
+      end
+
+      def redis
+        @redis ||= Redis.new(url: ENV.fetch("REDIS_URL", "redis://localhost:6379/0"))
+      end
+    end
+  end
+end