feat: Replace anchor tags with button elements for close actions in multiple managers to improve accessibility and semantic HTML

frontend/src/ServerManager.jsx

@@ -428,7 +428,7 @@ function ServerManager() {
               {error}
             </div>
           </div>
-          <a className="btn-close" onClick={() => setError('')}></a>
+          <button type="button" className="btn-close" onClick={() => setError('')}></button>
         </div>
       )}
       
@@ -442,7 +442,7 @@ function ServerManager() {
               {success}
             </div>
           </div>
-          <a className="btn-close" onClick={() => setSuccess('')}></a>
+          <button type="button" className="btn-close" onClick={() => setSuccess('')}></button>
         </div>
       )}
 
@@ -760,9 +760,9 @@ function ServerManager() {
           <div className="card-header">
             <h3 className="card-title mb-0">Существующие связи ({connections.length})</h3>
           </div>
-          <div className="card-body">
-            <div className="table-responsive">
-              <table className="table table-vcenter">
+            <div className="card-body">
+              <div className="table-responsive">
+                <table className="table card-table table-vcenter table-nowrap mb-0">
                 <thead>
                   <tr>
                     <th>Сервер A</th>