Improve admin page structure and styling for clarity

Updated the Admin Users Page by reorganizing sections, improving labels, and adding descriptions for better usability. Adjusted styles to enhance visual hierarchy and provide consistent spacing and formatting throughout.

frontend/src/styles.css

@@ -981,18 +981,47 @@ td {
 
 .admin-settings-page h2 {
   margin-top: 4px;
-  margin-bottom: 14px;
+  margin-bottom: 4px;
 }
 
 .admin-settings-page h3 {
   margin-top: 0;
-  margin-bottom: 10px;
+  margin-bottom: 2px;
+}
+
+.admin-page-subtitle {
+  margin: 0 0 14px;
+}
+
+.admin-section-head {
+  margin-bottom: 12px;
+  padding-bottom: 10px;
+  border-bottom: 1px solid #264671;
+}
+
+.admin-section-head p {
+  margin: 4px 0 0;
+  font-size: 13px;
 }
 
 .admin-user-form {
   gap: 10px;
 }
 
+.admin-field label {
+  display: block;
+  margin-bottom: 6px;
+  color: #c6d7f1;
+  font-size: 13px;
+  font-weight: 600;
+}
+
+.admin-field input,
+.admin-field select {
+  width: 100%;
+  min-height: 38px;
+}
+
 .admin-users-table-wrap table tbody .admin-user-row td {
   padding-top: 11px;
   padding-bottom: 11px;
@@ -1045,6 +1074,7 @@ td {
 
 .admin-test-recipient {
   min-width: 260px;
+  max-width: 320px;
 }
 
 .muted {