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/mcp_server/tools/helpers.py

@@ -0,0 +1,59 @@
+"""
+Hilfsfunktionen für MCP-Tool-Implementierungen.
+"""
+
+from __future__ import annotations
+
+import json
+from datetime import date, datetime, time
+from decimal import Decimal
+from uuid import UUID
+
+
+def serialize_value(value):
+    """Konvertiert Django-Feldwerte in JSON-serialisierbare Typen."""
+    if isinstance(value, UUID):
+        return str(value)
+    if isinstance(value, Decimal):
+        return float(value)
+    if isinstance(value, (date, datetime)):
+        return value.isoformat()
+    if isinstance(value, time):
+        return value.isoformat()
+    return value
+
+
+def model_to_dict(instance, fields=None, exclude=None) -> dict:
+    """
+    Konvertiert eine Django-Model-Instanz in ein serialisierbares Dict.
+
+    Args:
+        instance: Django Model Instanz
+        fields: Nur diese Felder einschließen (None = alle)
+        exclude: Diese Felder ausschließen
+    """
+    exclude = exclude or []
+    result = {}
+    for field in instance._meta.fields:
+        name = field.name
+        if fields and name not in fields:
+            continue
+        if name in exclude:
+            continue
+        value = getattr(instance, name)
+        # ForeignKey: _id-Suffix-Wert (nicht ganzes Objekt)
+        result[name] = serialize_value(value)
+
+    # Auch ForeignKey-IDs explizit aufnehmen (z.B. konto_id)
+    for field in instance._meta.fields:
+        if hasattr(field, "attname") and field.attname != field.name:
+            attname = field.attname
+            if attname not in result:
+                result[attname] = serialize_value(getattr(instance, attname))
+
+    return result
+
+
+def format_result(data) -> str:
+    """Gibt Daten als formatiertes JSON zurück."""
+    return json.dumps(data, ensure_ascii=False, indent=2, default=str)