feat(cloud-files): Geteilte Ordner + Rechtsklick-Menue

Backend:
- /api/sync/tree liefert jetzt {tree, shared} - shared enthaelt alle
  Dateien die MIT dem Benutzer geteilt wurden (FilePermission), nur
  Top-Level-Shares, mit Owner-Name im Anzeigenamen
- updated_at zusaetzlich als modified_at im Response fuer Client-
  Kompatibilitaet

Client:
- fetch_remote_entries merged Shared-Subtree unter virtuellem Ordner
  "Geteilt mit mir" (synthetische ID -1) in den Mount-Point
- modified_at faellt auf updated_at zurueck, falls nicht vorhanden

Kontextmenue:
- Neue HKCU-Registry-Eintraege fuer "Immer offline verfuegbar" und
  "Speicher freigeben", AppliesTo filtert auf Mount-Pfad, sodass die
  Verben nur bei Dateien unterhalb des Sync-Ordners erscheinen
- Aufruf der eigenen .exe mit --pin / --unpin <file>
- handle_cli_shortcuts fuehrt die Aktion aus und beendet sofort,
  ohne die UI/Tray/Single-Instance-Logik anzustossen

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

backend/app/api/files.py

@@ -1254,32 +1254,79 @@ def list_locks():
 @api_bp.route('/sync/tree', methods=['GET'])
 @token_required
 def sync_tree():
-    """Returns complete file tree with checksums for sync clients."""
+    """Returns complete file tree with checksums for sync clients.
+
+    Includes both files owned by the user (under 'tree') and files
+    shared WITH the user (as a virtual 'Geteilt mit mir' folder under
+    'shared'). The client merges both.
+    """
     user = request.current_user
 
+    def _entry(f):
+        entry = {
+            'id': f.id,
+            'name': f.name,
+            'is_folder': f.is_folder,
+            'size': f.size,
+            'checksum': f.checksum,
+            'updated_at': f.updated_at.isoformat() if f.updated_at else None,
+            'modified_at': f.updated_at.isoformat() if f.updated_at else None,
+        }
+        lock = FileLock.get_lock(f.id)
+        if lock:
+            entry['locked'] = True
+            entry['locked_by'] = lock.user.username
+        return entry
+
     def _build_tree(parent_id):
         files = File.query.filter_by(owner_id=user.id, parent_id=parent_id, is_trashed=False)\
             .order_by(File.is_folder.desc(), File.name).all()
         result = []
         for f in files:
-            entry = {
-                'id': f.id,
-                'name': f.name,
-                'is_folder': f.is_folder,
-                'size': f.size,
-                'checksum': f.checksum,
-                'updated_at': f.updated_at.isoformat() if f.updated_at else None,
-            }
-            lock = FileLock.get_lock(f.id)
-            if lock:
-                entry['locked'] = True
-                entry['locked_by'] = lock.user.username
+            e = _entry(f)
             if f.is_folder:
-                entry['children'] = _build_tree(f.id)
-            result.append(entry)
+                e['children'] = _build_tree(f.id)
+            result.append(e)
         return result
 
-    return jsonify({'tree': _build_tree(None)}), 200
+    def _build_shared_children(parent_id):
+        files = File.query.filter_by(parent_id=parent_id, is_trashed=False)\
+            .order_by(File.is_folder.desc(), File.name).all()
+        out = []
+        for f in files:
+            e = _entry(f)
+            if f.is_folder:
+                e['children'] = _build_shared_children(f.id)
+            out.append(e)
+        return out
+
+    shared_perms = FilePermission.query.filter_by(user_id=user.id).all()
+    shared_roots = []
+    seen = set()
+    for perm in shared_perms:
+        f = perm.file
+        if not f or f.is_trashed or f.id in seen:
+            continue
+        seen.add(f.id)
+        # Nur "Top-Level"-Shares: wenn der Eltern-Ordner NICHT auch geteilt
+        # ist, ist dieses Item die Wurzel des Shares beim Empfaenger.
+        parent_shared = any(
+            p.file_id == f.parent_id for p in shared_perms
+        ) if f.parent_id else False
+        if parent_shared:
+            continue
+        e = _entry(f)
+        owner = f.owner.display_name if hasattr(f, 'owner') and f.owner else None
+        if owner:
+            e['name'] = f'{f.name} (von {owner})'
+        if f.is_folder:
+            e['children'] = _build_shared_children(f.id)
+        shared_roots.append(e)
+
+    return jsonify({
+        'tree': _build_tree(None),
+        'shared': shared_roots,
+    }), 200
 
 
 @api_bp.route('/sync/events', methods=['GET'])