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/models/stream_node.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+# Nodo streaming (MediaMTX [+ relay ffmpeg]). Fase 0: registry + assignment URL.
+class StreamNode < ApplicationRecord
+  ROLES = %w[home cloud lab].freeze
+  STATUSES = %w[provisioning ready draining offline error].freeze
+  PROVIDERS = %w[local proxmox_lab hetzner].freeze
+
+  has_many :stream_sessions, dependent: :nullify
+
+  validates :slug, presence: true, uniqueness: true
+  validates :hostname, presence: true
+  validates :role, inclusion: { in: ROLES }
+  validates :status, inclusion: { in: STATUSES }
+  validates :provider, inclusion: { in: PROVIDERS }
+  validates :rtmp_base_url, :hls_base_url, :api_base_url, presence: true
+  validates :max_publishers, :max_relays, numericality: { greater_than: 0 }
+
+  scope :ready, -> { where(status: "ready") }
+  scope :allocatable, -> { ready }
+
+  # Sessioni che occupano uno slot path MediaMTX su questo nodo.
+  def occupying_sessions
+    stream_sessions.where(status: %w[idle connecting live reconnecting paused])
+  end
+
+  def active_publishers
+    occupying_sessions.count
+  end
+
+  def free_slots
+    [max_publishers - active_publishers, 0].max
+  end
+
+  def allocatable?
+    status == "ready" && free_slots.positive?
+  end
+end