Aggiunge overlay server-side burn-in e stabilizza diretta live.

Tabellone, badge e brand sono ricodificati nel flusso _air via OverlayRelay;
sync punteggio HTTP, volume condiviso rails/sidekiq, qualità 720p migliorata
e badge CONNECTING in ripresa da pausa.

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

backend/app/services/recordings/upload_from_session.rb

@@ -64,8 +64,11 @@ module Recordings
       @merged_temp_path = File.join(Dir.tmpdir, "replay-#{@session.id}-#{SecureRandom.hex(4)}.mp4")
       list_path = "#{@merged_temp_path}.txt"
       File.write(list_path, source_files.map { |f| "file '#{f.gsub("'", "'\\''")}'" }.join("\n"))
-      success = system("ffmpeg", "-y", "-f", "concat", "-safe", "0", "-i", list_path, "-c", "copy", @merged_temp_path,
-                       out: File::NULL, err: File::NULL)
+      success = system(
+        "ffmpeg", "-y", "-f", "concat", "-safe", "0", "-i", list_path,
+        "-c", "copy", "-movflags", "+faststart", @merged_temp_path,
+        out: File::NULL, err: File::NULL
+      )
       FileUtils.rm_f(list_path)
       raise Error, "Impossibile unire i segmenti video" unless success && File.exist?(@merged_temp_path)