refactor(backup): move .picpeak download to the Dashboard tab

Downloading a portable backup is a "make a backup" action, so it belongs
next to "Run Backup Now" on the Dashboard, not under Restore. Split the
combined card into PicpeakExportCard (Dashboard) and PicpeakRestoreCard
(Restore). The manifest stays bundled inside the .picpeak, so there is no
separate manifest-only download for the portable format.

frontend/src/pages/admin/BackupManagement.tsx

@@ -23,7 +23,7 @@ import { BackupDashboard } from '../../components/admin/BackupDashboard';
 import { BackupConfiguration } from '../../components/admin/BackupConfiguration';
 import { BackupHistory } from '../../components/admin/BackupHistory';
 import { RestoreWizard } from '../../components/admin/RestoreWizard';
-import { PicpeakBackupCard } from '../../components/admin/PicpeakBackupCard';
+import { PicpeakExportCard, PicpeakRestoreCard } from '../../components/admin/PicpeakBackupCard';
 import { BackupIntegrityCard } from '../../components/admin/BackupIntegrityCard';
 import { BackupCoverageCard } from '../../components/admin/BackupCoverageCard';
 import { api } from '../../config/api';
@@ -205,12 +205,15 @@ export const BackupManagement: React.FC = () => {
       {/* Tab Content */}
       <div className="mt-6">
         {activeTab === 'dashboard' && (
-          <BackupDashboard
-            status={backupStatus}
-            config={backupConfig}
-            onRunBackup={() => manualBackupMutation.mutate()}
-            isBackupRunning={backupStatus?.isRunning || manualBackupMutation.isPending}
-          />
+          <div className="space-y-6">
+            <BackupDashboard
+              status={backupStatus}
+              config={backupConfig}
+              onRunBackup={() => manualBackupMutation.mutate()}
+              isBackupRunning={backupStatus?.isRunning || manualBackupMutation.isPending}
+            />
+            <PicpeakExportCard />
+          </div>
         )}
 
         {activeTab === 'configuration' && (
@@ -227,7 +230,7 @@ export const BackupManagement: React.FC = () => {
 
         {activeTab === 'restore' && (
           <div className="space-y-6">
-            <PicpeakBackupCard />
+            <PicpeakRestoreCard />
             <RestoreWizard onVerifyIntegrity={() => setActiveTab('integrity')} />
           </div>
         )}