Riduce reload MediaMTX in live e allinea ingest mobile al preset qualità.

Evita patch recording ripetute che distruggevano i muxer HLS (500 ops) e fa encoderare 1080p/720p con codec e bitrate coerenti al wizard.

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

backend/app/services/sessions/select_quality.rb

@@ -2,6 +2,7 @@ module Sessions
   # Sceglie il preset più alto supportato dall'upload misurato (test rete).
   class SelectQuality
     UPLOAD_HEADROOM = 0.8
+    UPLOAD_HEADROOM_1080P = 1.0
 
     PRESETS = [
       { id: "1080p_30_4.5mbps", target_bitrate: 4_500_000, target_fps: 30 },
@@ -23,7 +24,8 @@ module Sessions
     end
 
     def upload_sufficient?(preset)
-      @upload_mbps >= (preset[:target_bitrate] / 1_000_000.0 * UPLOAD_HEADROOM)
+      headroom = preset[:id].start_with?("1080p") ? UPLOAD_HEADROOM_1080P : UPLOAD_HEADROOM
+      @upload_mbps >= (preset[:target_bitrate] / 1_000_000.0 * headroom)
     end
   end
 end