feat(App): implement mobile sidebar overlay with backdrop and responsive adjustments; enhance layout for better usability on small screens

frontend/src/components/TopNStats.jsx

@@ -58,9 +58,9 @@ function TopNStats({ data, loading }) {
   };
 
   return (
-    <div className="row g-3">
+    <div className="row g-2 g-md-3">
       {/* Top Страны */}
-      <div className="col-md-6">
+      <div className="col-12 col-md-6">
         <div className="card h-100">
           <div className="card-header">
             <h3 className="card-title">
@@ -107,7 +107,7 @@ function TopNStats({ data, loading }) {
       </div>
 
       {/* Top Провайдеры */}
-      <div className="col-md-6">
+      <div className="col-12 col-md-6">
         <div className="card h-100">
           <div className="card-header">
             <h3 className="card-title">