feat: supprimer le checkbox Débloquer devenu inutile (closes #15)

Le serveur Python gère nativement le cleanup des sessions orphelines
au login — plus besoin de forceDisconnect côté client.

styles-modern.css

@@ -227,96 +227,6 @@ body {
     font-size: 14px;
 }
 
-/* Checkbox de déconnexion forcée */
-.force-disconnect-container {
-    margin: 25px 0 20px 0;
-    padding: 16px;
-    background: #f8f9fa;
-    border-radius: 8px;
-    border: 1px solid #e9ecef;
-    transition: all 0.2s ease;
-}
-
-.force-disconnect-container:hover {
-    border-color: #dee2e6;
-    background: #f1f3f5;
-}
-
-.checkbox-label {
-    display: flex;
-    align-items: flex-start;
-    cursor: pointer;
-    user-select: none;
-    font-size: 14px;
-    color: #333;
-    position: relative;
-}
-
-.checkbox-label input[type="checkbox"] {
-    position: absolute;
-    opacity: 0;
-    cursor: pointer;
-    height: 18px;
-    width: 18px;
-    left: 0;
-    top: 1px;
-    z-index: 1;
-}
-
-.checkbox-label::before {
-    content: '';
-    display: inline-block;
-    width: 18px;
-    height: 18px;
-    margin-right: 12px;
-    margin-top: 1px;
-    border: 2px solid #dee2e6;
-    border-radius: 4px;
-    background: white;
-    transition: all 0.2s ease;
-    flex-shrink: 0;
-}
-
-.checkbox-label input[type="checkbox"]:checked + span::before {
-    content: '';
-    position: absolute;
-    left: 0;
-    top: 1px;
-    width: 18px;
-    height: 18px;
-    background: #667eea;
-    border: 2px solid #667eea;
-    border-radius: 4px;
-}
-
-.checkbox-label input[type="checkbox"]:checked + span::after {
-    content: '';
-    position: absolute;
-    left: 6px;
-    top: 4px;
-    width: 6px;
-    height: 11px;
-    border: solid white;
-    border-width: 0 2px 2px 0;
-    transform: rotate(45deg);
-}
-
-.checkbox-label span {
-    font-weight: 600;
-    color: #495057;
-    letter-spacing: 0.3px;
-    padding-top: 1px;
-}
-
-.checkbox-hint {
-    display: block;
-    margin-top: 6px;
-    margin-left: 30px;
-    font-size: 13px;
-    color: #6c757d;
-    line-height: 1.5;
-}
-
 /* === PAGE PRINCIPALE === */
 #mainPage {
     flex-direction: column;