v4.1.0: DMS email documents, category-specific Nachweis linking, version system

- Save cover email body as DMS document with new 'email' context type
- Show email body separately from attachments in email detail view
- Add per-category DMS document assignment in quarterly confirmation
  (Studiennachweis, Einkommenssituation, Vermögenssituation)
- Add VERSION file and context processor for automatic version display
- Add MCP server, agent system, import/export, and new migrations
- Update compose files and production environment template

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/stiftung/urls.py

@@ -1,15 +1,23 @@
-from django.urls import path
+from django.urls import include, path
 
 from . import views
 
 app_name = "stiftung"
 
 urlpatterns = [
+    # AI Agent
+    path("agent/", include("stiftung.agent.urls")),
+
     # Home - Main landing page after login
     path("", views.home, name="home"),
-    # CSV Import URLs
+    # CSV Import URLs (legacy)
     path("import/", views.csv_import_list, name="csv_import_list"),
     path("import/neu/", views.csv_import_create, name="csv_import_create"),
+    # Unified Import/Export Hub
+    path("daten/", views.import_export_hub, name="import_export_hub"),
+    path("daten/export/", views.csv_export, name="csv_export"),
+    path("daten/import/upload/", views.csv_import_upload, name="csv_import_upload"),
+    path("daten/import/ausfuehren/", views.csv_import_execute, name="csv_import_execute"),
     # Destinatär URLs (Förderungsempfänger)
     path("destinataere/", views.destinataer_list, name="destinataer_list"),
     path(