feat: Kontakt-Ordner mit Drag&Drop Baum (wie KI-Chat Sidebar)

- Backend: ContactFolder model (hierarchisch, parent_id, sort_order)
- Migration 0022: contact_folders Tabelle + folder_id FK auf contacts
- CRUD Routes: /api/v1/contact-folders (list, create, update, delete, reorder)
- Move Contact API: /api/v1/contact-folders/contacts/{id}/move
- folder_id Filter in contacts list API
- Frontend: ContactFolderTree mit Baum-Struktur, Drag&Drop, Kontext-Menü
- Kontakt-Personen-Icon statt Ordner-Symbol
- ContactList Items draggable (List/Table/Cards View)
- React Query Hooks für Folder CRUD + Move Contact
- Alle 266 Frontend-Tests passing

app/main.py

@@ -29,6 +29,7 @@ from app.routes import (
     audit,
     auth,
     companies,
+    contact_folders,
     contacts,
     groups,
     health,
@@ -230,6 +231,7 @@ def create_app() -> FastAPI:
     app.include_router(notifications.router)
     app.include_router(companies.router)
     app.include_router(contacts.router)
+    app.include_router(contact_folders.router)
     app.include_router(import_export.router)
     app.include_router(plugins.router)
     app.include_router(ai_copilot.router)