feat(backup): UI for backup-integrity verifier — tab + post-restore CTA

Frontend half of the diagnostic shipped in 4812fcd. Adds:
  - BackupIntegrityCard component — runs the check on demand, surfaces
    the five summary counters (total / verifiedOk / existsButNoHash /
    missing / hashMismatches), and expands collapsible result tables
    for missing files + hash mismatches. existsButNoHash is exposed as
    a separate amber-toned bucket so admins can distinguish hash-
    verified evidence from existence-only at a glance — the latter is
    explicitly weaker in a legal dispute and the UI says so.
  - "Integrity" tab on BackupManagement, alongside the existing
    Dashboard / Configuration / History / Restore tabs. Card is
    portable — when the System Health page (backlog item) lands it
    can lift the component without changes.
  - Post-restore CTA on the RestoreWizard success card (D2 follow-
    through): "Verify document integrity now" button that switches
    the parent tab to Integrity. The audit trail captured at sign /
    issue time is worth nothing if the documents it refers to are
    missing from the restored copy — verifier surfaces that drift
    in one click before the admin trusts the restored state.
i18n strings added in EN + DE (per user_languages — only those two
are native; other locales fall back to the English defaults and
should be flagged for native-speaker review per
feedback_translation_flagging if anyone picks them up).

frontend/src/services/admin.service.ts

@@ -201,6 +201,50 @@ export interface Activity {
   createdAt: string;
 }
 
+// Backup-integrity verifier — diagnostic endpoint that walks every
+// CRM document-artefact path column and confirms files exist on disk
+// (plus SHA-256 match where the schema stores one). Mirrors the
+// shape returned by backupIntegrityService.verifyDocumentArtefacts.
+export type BackupIntegrityScope =
+  | 'quote'
+  | 'contract'
+  | 'contract-signature'
+  | 'invoice';
+
+export interface BackupIntegrityMissingRow {
+  table: string;
+  rowId: number;
+  column: string;
+  expectedPath: string;
+}
+
+export interface BackupIntegrityHashMismatchRow extends BackupIntegrityMissingRow {
+  expectedSha: string;
+  actualSha: string;
+}
+
+export interface BackupIntegrityExistsButNoHashRow {
+  table: string;
+  rowId: number;
+  column: string;
+  path: string;
+}
+
+export interface BackupIntegrityReport {
+  scannedAt: string;
+  scopes: BackupIntegrityScope[];
+  summary: {
+    totalRows: number;
+    verifiedOk: number;
+    missingFiles: number;
+    hashMismatches: number;
+    existsButNoHash: number;
+  };
+  missing: BackupIntegrityMissingRow[];
+  hashMismatches: BackupIntegrityHashMismatchRow[];
+  existsButNoHash: BackupIntegrityExistsButNoHashRow[];
+}
+
 export interface AdminProfile {
   id: number;
   username: string;
@@ -262,6 +306,19 @@ export const adminService = {
     return response.data;
   },
 
+  // Backup-integrity verifier (read-only diagnostic). `scope` filters
+  // which document classes to walk; omit for a full scan.
+  async getBackupIntegrity(
+    scope?: BackupIntegrityScope[],
+  ): Promise<BackupIntegrityReport> {
+    const params = scope && scope.length > 0 ? { scope: scope.join(',') } : undefined;
+    const response = await api.get<{ report: BackupIntegrityReport }>(
+      '/admin/system-health/backup-integrity',
+      { params },
+    );
+    return response.data.report;
+  },
+
   // Format activity message
   formatActivityMessage(activity: Activity): string {
     // Feature-flag toggles carry a `changed` diff in metadata. Render