feat(export): Obsidian-compatible Markdown vault as streamed ZIP

- GET /export/markdown streams the workspace as ZIP (no temp files):
  notes as .md with YAML front matter in the user's folder structure
  (shared notes and mounted folders included, empty folders kept)
- Clean Markdown: top-level headings/dividers/callouts/code as real blocks
  (their children move up a level), lists with tabs, todos as - [ ]
- Aufgaben/<list>.md in Obsidian Tasks format (due date, priority,
  subtasks, notes), Listen/<list>.md for shopping and other lists
- Safe, unique file names; download button in settings (mobile-safe)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/settings/UserSettingsView.tsx

@@ -362,17 +362,38 @@ export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
     setTimeout(() => setCopiedLabel(null), 2000);
   };
 
+  // Works on mobile browsers too: the link must be in the document and the URL alive until the click ran
+  const saveBlob = (blob: Blob, filename: string) => {
+    const url = URL.createObjectURL(blob);
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = filename;
+    document.body.appendChild(a);
+    a.click();
+    a.remove();
+    window.setTimeout(() => URL.revokeObjectURL(url), 10000);
+  };
+
   const handleExportData = async () => {
     const data = await api.exportAll();
     const blob = new Blob([JSON.stringify(data, null, 2)], {
       type: 'application/json;charset=utf-8',
     });
-    const url = URL.createObjectURL(blob);
-    const a = document.createElement('a');
-    a.href = url;
-    a.download = `mindsift-backup-${new Date().toISOString().slice(0, 10)}.json`;
-    a.click();
-    URL.revokeObjectURL(url);
+    saveBlob(blob, `mindsift-backup-${new Date().toISOString().slice(0, 10)}.json`);
+  };
+
+  const [exportingVault, setExportingVault] = useState(false);
+  const [vaultError, setVaultError] = useState<string | null>(null);
+  const handleExportVault = async () => {
+    setExportingVault(true);
+    setVaultError(null);
+    try {
+      saveBlob(await api.exportMarkdownVault(), `mindsift-vault-${new Date().toISOString().slice(0, 10)}.zip`);
+    } catch (err: any) {
+      setVaultError(err.message || 'Export fehlgeschlagen');
+    } finally {
+      setExportingVault(false);
+    }
   };
 
   const baseUrl = window.location.origin;
@@ -1230,6 +1251,28 @@ export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
                   <span>Backup herunterladen</span>
                 </button>
               </div>
+
+              {/* Obsidian-compatible Markdown vault */}
+              <div className="pt-4 border-t border-border flex flex-col sm:flex-row sm:items-center justify-between gap-3">
+                <div>
+                  <h3 className="font-bold text-main">Markdown-Archiv für Obsidian (.zip)</h3>
+                  <p className="text-muted text-[11px]">
+                    Alle Notizen als <code className="font-mono">.md</code>-Dateien in deiner Ordnerstruktur (mit Titel, Tags und
+                    Datum im Kopf), Aufgaben je Liste unter <code className="font-mono">Aufgaben/</code> im Format des
+                    Obsidian-Tasks-Plugins, Listen unter <code className="font-mono">Listen/</code>. Mit dir geteilte Notizen sind
+                    dabei.
+                  </p>
+                  {vaultError && <p className="text-[11px] text-status-err mt-1">{vaultError}</p>}
+                </div>
+                <button
+                  onClick={handleExportVault}
+                  disabled={exportingVault}
+                  className="btn-action h-11 sm:h-9 px-4 text-xs flex items-center justify-center gap-2 flex-shrink-0 disabled:opacity-50"
+                >
+                  <Download className="w-3.5 h-3.5 text-accent" />
+                  <span>{exportingVault ? 'Wird erstellt…' : 'Markdown-Archiv herunterladen'}</span>
+                </button>
+              </div>
             </div>
           )}
         </div>