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/spec/services/streams/dns_providers/hetzner_spec.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Streams::DnsProviders::Hetzner do
+  let(:stubs) { Faraday::Adapter::Test::Stubs.new }
+  let(:conn) do
+    Faraday.new(url: "https://api.hetzner.cloud/v1") do |f|
+      f.request :json
+      f.response :json
+      f.adapter :test, stubs
+    end
+  end
+  let(:provider) { described_class.new(token: "test-token", zone: "mltv-stream.net", conn: conn) }
+
+  after { stubs.verify_stubbed_calls }
+
+  it "upserts an A record (delete then create)" do
+    stubs.delete("/zones/mltv-stream.net/rrsets/ingest-01/A") { [404, {}, ""] }
+    stubs.post("/zones/mltv-stream.net/rrsets") do |env|
+      body = JSON.parse(env.body)
+      expect(body["name"]).to eq("ingest-01")
+      expect(body["type"]).to eq("A")
+      expect(body["records"].first["value"]).to eq("49.13.1.2")
+      [201, { "Content-Type" => "application/json" }, { "rrset" => { "name" => "ingest-01" } }]
+    end
+
+    expect(provider.upsert_a("ingest-01.mltv-stream.net", "49.13.1.2")).to eq(true)
+  end
+
+  it "deletes an A record" do
+    stubs.delete("/zones/mltv-stream.net/rrsets/ingest-01/A") { [204, {}, ""] }
+    expect(provider.delete_a("ingest-01.mltv-stream.net")).to eq(true)
+  end
+end