Fix freeze YouTube al cambio punteggio: PNG atomica e relay stabile

rsvg scrive su .tmp poi rename; il feeder ignora PNG parziali.
YouTube relay: no doppio avvio, reconnect RTMP; overlay restart solo dopo 3 miss.

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

backend/app/services/streams/youtube_relay.rb

@@ -12,6 +12,8 @@ module Streams
         return if session.stream_key.blank?
         return if session.terminal?
 
+        return pid_for(session.id).to_i if running?(session.id)
+
         stop(session) if pid_for(session.id).present?
 
         log_path = log_file(session)
@@ -80,6 +82,7 @@ module Streams
           "-fflags", "+genpts+discardcorrupt", "-use_wallclock_as_timestamps", "1",
           "-analyzeduration", "10000000", "-probesize", "10000000",
           "-rw_timeout", "15000000",
+          "-reconnect", "1", "-reconnect_at_eof", "1", "-reconnect_streamed", "1", "-reconnect_delay_max", "5",
           "-i", intake,
           "-f", "lavfi", "-i", "anullsrc=channel_layout=mono:sample_rate=48000",
           "-map", "0:v:0", "-map", "1:a:0",