Stabilizza live YouTube/RTMP e fix crash rotazione mobile.

Pipeline YouTube con relay, overlay e publisher sync lato backend; fix GL pauseGlDuringRotation su Android per evitare crash in rotazione durante lo streaming Flutter.

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

backend/app/services/youtube/api_throttle.rb

@@ -0,0 +1,28 @@
+module Youtube
+  # Evita tempeste di chiamate YouTube Data API (quota / userRequestsExceedRateLimit).
+  class ApiThrottle
+    KEY = "youtube_api:rate_limited_until"
+
+    class << self
+      def rate_limited?
+        until_ts = redis.get(KEY).to_i
+        until_ts.positive? && until_ts > Time.now.to_i
+      end
+
+      def mark_rate_limited!(seconds: 120)
+        redis.set(KEY, (Time.now.to_i + seconds), ex: seconds + 30)
+      end
+
+      def rate_limit_error?(message)
+        msg = message.to_s
+        msg.include?("userRequestsExceedRateLimit") || msg.include?("rate limit")
+      end
+
+      private
+
+      def redis
+        @redis ||= Redis.new(url: ENV.fetch("REDIS_URL", "redis://localhost:6379/0"))
+      end
+    end
+  end
+end