fix: code quality and safety improvements

frontend/src/features/vault/components/CategoryManager.tsx

@@ -825,7 +825,7 @@ const OrganizationModal: React.FC<OrganizationModalProps> = ({
                 ) : (
                   <div className="w-full h-full bg-gradient-to-br from-zinc-200 to-zinc-300 dark:from-zinc-700 dark:to-zinc-800 rounded-lg flex items-center justify-center">
                     <span className="text-zinc-500 dark:text-zinc-400 font-bold text-2xl">
-                      {newOrg.name ? newOrg.name.charAt(0).toUpperCase() : '?'}
+                      {newOrg.name ? newOrg.name[0].toUpperCase() : '?'}
                     </span>
                   </div>
                 )}

frontend/src/features/vault/components/OrganizationCard.tsx

@@ -186,7 +186,7 @@ const OrganizationCard: React.FC<OrganizationCardProps> = ({ org, onDelete, onEd
           // Fallback: First letter
           <div className="w-12 h-12 sm:w-14 sm:h-14 bg-gradient-to-br from-blue-500/20 to-blue-600/10 border border-blue-500/20 rounded-lg sm:rounded-xl flex items-center justify-center">
             <span className="text-lg sm:text-xl font-bold text-blue-400">
-              {org.name.charAt(0).toUpperCase()}
+              {org.name[0].toUpperCase()}
             </span>
           </div>
         )}

frontend/src/features/vault/components/VaultListItem.tsx

@@ -168,7 +168,7 @@ const VaultListItem: React.FC<VaultListItemProps> = ({ org, onClick, onEdit, onD
         ) : (
           <div className="w-8 h-8 sm:w-10 sm:h-10 bg-gradient-to-br from-blue-500/20 to-blue-600/10 border border-blue-500/20 rounded-lg flex items-center justify-center">
             <span className="text-sm sm:text-base font-bold text-blue-400">
-              {org.name.charAt(0).toUpperCase()}
+              {org.name[0].toUpperCase()}
             </span>
           </div>
         )}

frontend/src/features/vault/hooks/useExport.ts

@@ -148,7 +148,7 @@ export function useExport(): UseExportReturn {
    */
   const exportVault = useCallback(async (password: string, format: ExportFormat) => {
     // Validate inputs
-    if (!password || password.trim() === '') {
+    if (!password || password.trim().length === 0) {
       setError('Password is required');
       setPhase('ERROR');
       return;

frontend/src/utils/encryption.ts

@@ -128,7 +128,7 @@ export async function encryptData(
   plaintext: string,
   key: CryptoKey
 ): Promise<{ iv: string; ciphertext: string }> {
-  if (!plaintext || plaintext.trim() === '') {
+  if (!plaintext || plaintext.trim().length === 0) {
     throw new Error('Cannot encrypt empty data');
   }