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/streams/overlay/refresh.rb

@@ -0,0 +1,48 @@
+module Streams
+  module Overlay
+    class Refresh
+      class Error < StandardError; end
+
+      def self.call(session)
+        new(session).call
+      end
+
+      def initialize(session)
+        @session = session.reload
+      end
+
+      def call
+        return false if @session.terminal?
+
+        dir = Streams::Overlay.overlay_dir(@session.id)
+        FileUtils.mkdir_p(dir)
+        badge = BadgeLabel.for(@session)
+        svg = SvgBuilder.new(@session, badge: badge).to_svg
+        svg_path = dir.join("overlay.svg")
+        png_path = Streams::Overlay.overlay_png_path(@session)
+        atomic_write(svg_path, svg)
+        render_png!(svg_path, png_path)
+        true
+      rescue StandardError => e
+        Rails.logger.warn("[Overlay::Refresh] session=#{@session.id} #{e.class}: #{e.message}")
+        false
+      end
+
+      private
+
+      def atomic_write(path, content)
+        tmp = "#{path}.tmp"
+        File.write(tmp, content)
+        File.rename(tmp, path)
+      end
+
+      def render_png!(svg_path, png_path)
+        unless system("rsvg-convert", "-w", "1280", "-h", "720", "-o", png_path.to_s, svg_path.to_s, out: File::NULL, err: File::NULL)
+          raise Error, "rsvg-convert fallito per session #{@session.id}"
+        end
+
+        FileUtils.touch(png_path)
+      end
+    end
+  end
+end