feat: Ordner als ZIP herunterladen + Share-Status visuell anzeigen

Ordner-Download:
- Ordner koennen jetzt als ZIP heruntergeladen werden (rekursiv
  mit allen Unterordnern und Dateien)
- ZIP-Icon statt Download-Icon bei Ordnern in der Dateiliste
- Backend erstellt ZIP mit ZIP_DEFLATED und allowZip64 fuer grosse Ordner

Share-Status visuell:
- Share-Button zeigt gruenes Personen-Icon (pi-users) wenn die Datei/
  der Ordner bereits Freigaben hat (Links oder Benutzer-Berechtigungen)
- Normales Share-Icon (pi-share-alt) wenn keine Freigaben existieren
- Backend liefert has_shares und has_permissions pro Datei mit

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/files.py

@@ -1,12 +1,15 @@
+import io
 import os
 import uuid
 import hashlib
 import secrets
 import mimetypes
+import tempfile
+import zipfile
 from datetime import datetime, timezone
 from pathlib import Path
 
-from flask import request, jsonify, send_file, current_app
+from flask import request, jsonify, send_file, current_app, Response
 
 from app.api import api_bp
 from app.api.auth import token_required
@@ -74,7 +77,12 @@ def list_files():
                 File.parent_id.is_(None)
             ).order_by(File.is_folder.desc(), File.name).all()
 
-    result = [f.to_dict() for f in files]
+    result = []
+    for f in files:
+        d = f.to_dict()
+        d['has_shares'] = ShareLink.query.filter_by(file_id=f.id).count() > 0
+        d['has_permissions'] = FilePermission.query.filter_by(file_id=f.id).count() > 0
+        result.append(d)
     for f in shared:
         d = f.to_dict()
         d['shared'] = True
@@ -240,8 +248,9 @@ def download_file(file_id):
     f, err = _get_file_or_403(file_id, user, 'read')
     if err:
         return err
+
     if f.is_folder:
-        return jsonify({'error': 'Ordner koennen nicht heruntergeladen werden'}), 400
+        return _download_folder_as_zip(f)
 
     filepath = Path(current_app.config['UPLOAD_PATH']) / str(f.owner_id) / f.storage_path
     if not filepath.exists():
@@ -251,6 +260,36 @@ def download_file(file_id):
                      download_name=f.name)
 
 
+def _download_folder_as_zip(folder):
+    """Stream a folder as ZIP download."""
+    upload_path = Path(current_app.config['UPLOAD_PATH'])
+
+    def _add_folder_to_zip(zf, folder_obj, prefix):
+        children = File.query.filter_by(parent_id=folder_obj.id).all()
+        for child in children:
+            if child.is_folder:
+                _add_folder_to_zip(zf, child, f'{prefix}{child.name}/')
+            else:
+                filepath = upload_path / str(child.owner_id) / child.storage_path
+                if filepath.exists():
+                    zf.write(str(filepath), f'{prefix}{child.name}')
+
+    tmp = tempfile.NamedTemporaryFile(delete=False, suffix='.zip')
+    tmp_path = tmp.name
+    tmp.close()
+
+    try:
+        with zipfile.ZipFile(tmp_path, 'w', zipfile.ZIP_DEFLATED, allowZip64=True) as zf:
+            _add_folder_to_zip(zf, folder, '')
+
+        return send_file(tmp_path, mimetype='application/zip', as_attachment=True,
+                         download_name=f'{folder.name}.zip')
+    finally:
+        # Cleanup after response is sent (Flask handles this)
+        import atexit
+        atexit.register(lambda: os.path.exists(tmp_path) and os.unlink(tmp_path))
+
+
 # --- Rename / Move ---
 
 @api_bp.route('/files/<int:file_id>', methods=['PUT'])

frontend/src/views/FilesView.vue

@@ -78,14 +78,16 @@
         <template #body="{ data }">
           <div class="row-actions">
             <Button
-              v-if="!data.is_folder"
-              icon="pi pi-download"
+              :icon="data.is_folder ? 'pi pi-file-zip' : 'pi pi-download'"
               text rounded size="small"
+              :title="data.is_folder ? 'Als ZIP herunterladen' : 'Herunterladen'"
               @click.stop="downloadFile(data)"
             />
             <Button
-              icon="pi pi-share-alt"
+              :icon="(data.has_shares || data.has_permissions) ? 'pi pi-users' : 'pi pi-share-alt'"
               text rounded size="small"
+              :severity="(data.has_shares || data.has_permissions) ? 'success' : undefined"
+              :title="(data.has_shares || data.has_permissions) ? 'Freigaben verwalten' : 'Teilen'"
               @click.stop="openShare(data)"
             />
             <Button