feat: add duplicate handling features and UI elements for cipher management

webapp/src/components/vault/VaultListPanel.tsx

@@ -43,6 +43,7 @@ interface VaultListPanelProps {
   onSelectSortMode: (value: VaultSortMode) => void;
   onSyncVault: () => void;
   onOpenBulkDelete: () => void;
+  onSelectDuplicates: () => void;
   onSelectAll: () => void;
   onToggleCreateMenu: () => void;
   onStartCreate: (type: number) => void;
@@ -104,6 +105,11 @@ export default function VaultListPanel(props: VaultListPanelProps) {
         <button type="button" className="btn btn-danger small" disabled={!props.selectedCount || props.busy} onClick={props.onOpenBulkDelete}>
           <Trash2 size={14} className="btn-icon" /> {props.sidebarFilter.kind === 'trash' ? t('txt_delete_permanently') : t('txt_delete_selected')}
         </button>
+        {props.sidebarFilter.kind === 'duplicates' && (
+          <button type="button" className="btn btn-secondary small" disabled={!props.filteredCiphers.length || props.busy} onClick={props.onSelectDuplicates}>
+            <Check size={14} className="btn-icon" /> {t('txt_select_duplicate_items')}
+          </button>
+        )}
         <button type="button" className="btn btn-secondary small" disabled={!props.filteredCiphers.length} onClick={props.onSelectAll}>
           <CheckCheck size={14} className="btn-icon" /> {t('txt_select_all')}
         </button>
@@ -133,7 +139,7 @@ export default function VaultListPanel(props: VaultListPanelProps) {
             <RefreshCw size={14} className="btn-icon" /> {t('txt_restore')}
           </button>
         )}
-        {props.selectedCount > 0 && props.sidebarFilter.kind !== 'trash' && (
+        {props.selectedCount > 0 && props.sidebarFilter.kind !== 'trash' && props.sidebarFilter.kind !== 'duplicates' && (
           <button type="button" className="btn btn-secondary small" disabled={props.busy} onClick={props.onOpenMove}>
             <FolderInput size={14} className="btn-icon" /> {t('txt_move')}
           </button>

webapp/src/components/vault/VaultSidebar.tsx

@@ -1,4 +1,5 @@
 import {
+  Copy,
   CreditCard,
   Folder as FolderIcon,
   FolderPlus,
@@ -50,6 +51,9 @@ export default function VaultSidebar(props: VaultSidebarProps) {
         <button type="button" className={`tree-btn ${props.sidebarFilter.kind === 'trash' ? 'active' : ''}`} onClick={() => props.onChangeFilter({ kind: 'trash' })}>
           <Trash2 size={14} className="tree-icon" /> <span className="tree-label">{t('txt_trash')}</span>
         </button>
+        <button type="button" className={`tree-btn ${props.sidebarFilter.kind === 'duplicates' ? 'active' : ''}`} onClick={() => props.onChangeFilter({ kind: 'duplicates' })}>
+          <Copy size={14} className="tree-icon" /> <span className="tree-label">{t('txt_duplicates')}</span>
+        </button>
       </div>
 
       <div className="sidebar-block">

webapp/src/components/vault/vault-page-helpers.tsx

@@ -17,6 +17,7 @@ export type SidebarFilter =
   | { kind: 'all' }
   | { kind: 'favorite' }
   | { kind: 'trash' }
+  | { kind: 'duplicates' }
   | { kind: 'type'; value: TypeFilter }
   | { kind: 'folder'; folderId: string | null };
 
@@ -124,6 +125,86 @@ export function websiteIconUrl(host: string): string {
   return `/icons/${encodeURIComponent(host)}/icon.png`;
 }
 
+function valueOrFallback(value: string | null | undefined): string {
+  return String(value || '');
+}
+
+export function buildCipherDuplicateSignature(cipher: Cipher): string {
+  const normalized = {
+    type: Number(cipher.type || 1),
+    folderId: cipher.folderId || null,
+    favorite: !!cipher.favorite,
+    reprompt: Number(cipher.reprompt || 0),
+    name: valueOrFallback(cipher.decName ?? cipher.name),
+    notes: valueOrFallback(cipher.decNotes ?? cipher.notes),
+    login: cipher.login
+      ? {
+          username: valueOrFallback(cipher.login.decUsername ?? cipher.login.username),
+          password: valueOrFallback(cipher.login.decPassword ?? cipher.login.password),
+          totp: valueOrFallback(cipher.login.decTotp ?? cipher.login.totp),
+          uris: (cipher.login.uris || []).map((uri) => ({
+            uri: valueOrFallback(uri.decUri ?? uri.uri),
+            match: uri.match ?? null,
+          })),
+          fido2Credentials: (cipher.login.fido2Credentials || []).map((credential) => ({
+            creationDate: valueOrFallback(credential.creationDate),
+          })),
+        }
+      : null,
+    card: cipher.card
+      ? {
+          cardholderName: valueOrFallback(cipher.card.decCardholderName ?? cipher.card.cardholderName),
+          number: valueOrFallback(cipher.card.decNumber ?? cipher.card.number),
+          brand: valueOrFallback(cipher.card.decBrand ?? cipher.card.brand),
+          expMonth: valueOrFallback(cipher.card.decExpMonth ?? cipher.card.expMonth),
+          expYear: valueOrFallback(cipher.card.decExpYear ?? cipher.card.expYear),
+          code: valueOrFallback(cipher.card.decCode ?? cipher.card.code),
+        }
+      : null,
+    identity: cipher.identity
+      ? {
+          title: valueOrFallback(cipher.identity.decTitle ?? cipher.identity.title),
+          firstName: valueOrFallback(cipher.identity.decFirstName ?? cipher.identity.firstName),
+          middleName: valueOrFallback(cipher.identity.decMiddleName ?? cipher.identity.middleName),
+          lastName: valueOrFallback(cipher.identity.decLastName ?? cipher.identity.lastName),
+          username: valueOrFallback(cipher.identity.decUsername ?? cipher.identity.username),
+          company: valueOrFallback(cipher.identity.decCompany ?? cipher.identity.company),
+          ssn: valueOrFallback(cipher.identity.decSsn ?? cipher.identity.ssn),
+          passportNumber: valueOrFallback(cipher.identity.decPassportNumber ?? cipher.identity.passportNumber),
+          licenseNumber: valueOrFallback(cipher.identity.decLicenseNumber ?? cipher.identity.licenseNumber),
+          email: valueOrFallback(cipher.identity.decEmail ?? cipher.identity.email),
+          phone: valueOrFallback(cipher.identity.decPhone ?? cipher.identity.phone),
+          address1: valueOrFallback(cipher.identity.decAddress1 ?? cipher.identity.address1),
+          address2: valueOrFallback(cipher.identity.decAddress2 ?? cipher.identity.address2),
+          address3: valueOrFallback(cipher.identity.decAddress3 ?? cipher.identity.address3),
+          city: valueOrFallback(cipher.identity.decCity ?? cipher.identity.city),
+          state: valueOrFallback(cipher.identity.decState ?? cipher.identity.state),
+          postalCode: valueOrFallback(cipher.identity.decPostalCode ?? cipher.identity.postalCode),
+          country: valueOrFallback(cipher.identity.decCountry ?? cipher.identity.country),
+        }
+      : null,
+    sshKey: cipher.sshKey
+      ? {
+          privateKey: valueOrFallback(cipher.sshKey.decPrivateKey ?? cipher.sshKey.privateKey),
+          publicKey: valueOrFallback(cipher.sshKey.decPublicKey ?? cipher.sshKey.publicKey),
+          fingerprint: valueOrFallback(cipher.sshKey.decFingerprint ?? cipher.sshKey.keyFingerprint ?? cipher.sshKey.fingerprint),
+        }
+      : null,
+    secureNoteType: cipher.secureNote?.type ?? null,
+    fields: (cipher.fields || []).map((field) => ({
+      type: field.type ?? null,
+      name: valueOrFallback(field.decName ?? field.name),
+      value: valueOrFallback(field.decValue ?? field.value),
+      linkedId: field.linkedId ?? null,
+    })),
+    passwordHistory: (cipher.passwordHistory || []).map((entry) => ({
+      password: valueOrFallback(entry.password),
+      lastUsedDate: valueOrFallback(entry.lastUsedDate),
+    })),
+  };
+  return JSON.stringify(normalized);
+}
+
 export function createEmptyDraft(type: number): VaultDraft {
   return {
     type,