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_session.rb

@@ -7,6 +7,7 @@ class StreamSession < ApplicationRecord
 
   belongs_to :match
   belongs_to :user
+  belongs_to :stream_node, optional: true
   has_many :stream_events, dependent: :destroy
   has_one :score_state, dependent: :destroy
   has_many :device_states, dependent: :destroy
@@ -74,7 +75,7 @@ class StreamSession < ApplicationRecord
   def rtmp_ingest_url
     # RootEncoder richiede rtmp://host:port/app/stream (due segmenti).
     # MediaMTX path = live/match_{uuid} (no ?token= nel path).
-    "#{MatchLiveTv.mediamtx_rtmp_url}/#{mediamtx_path_name}"
+    "#{rtmp_base_url.chomp('/')}/#{mediamtx_path_name}"
   end
 
   def mediamtx_path_name
@@ -90,8 +91,29 @@ class StreamSession < ApplicationRecord
   end
 
   def hls_playback_url
-    base = MatchLiveTv.hls_public_url.chomp("/")
-    "#{base}/#{effective_hls_path_name}/index.m3u8"
+    "#{hls_base_url.chomp('/')}/#{effective_hls_path_name}/index.m3u8"
+  end
+
+  def rtmp_base_url
+    stream_node&.rtmp_base_url.presence || MatchLiveTv.mediamtx_rtmp_url
+  end
+
+  def hls_base_url
+    stream_node&.hls_base_url.presence || MatchLiveTv.hls_public_url
+  end
+
+  def mediamtx_api_base_url
+    stream_node&.api_base_url.presence || MatchLiveTv.mediamtx_api_url
+  end
+
+  def mediamtx_internal_rtmp_url
+    stream_node&.internal_rtmp_url.presence ||
+      ENV.fetch("MEDIAMTX_INTERNAL_RTMP_URL", "rtmp://mediamtx:1935")
+  end
+
+  def mediamtx_internal_hls_url
+    stream_node&.internal_hls_url.presence ||
+      ENV.fetch("MEDIAMTX_HLS_URL", "http://mediamtx:8888")
   end
 
   def effective_hls_path_name