Implementa pausa diretta con copertina slate e ripresa.

Metti in pausa ferma RTMP lato app mantenendo la camera aperta, MediaMTX
manda offline.mp4 agli spettatori e Chiudi termina definitivamente.

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

backend/app/models/stream_session.rb

@@ -54,7 +54,7 @@ class StreamSession < ApplicationRecord
     end
 
     event :pause do
-      transitions from: :live, to: :paused
+      transitions from: %i[live reconnecting], to: :paused
     end
 
     event :resume do