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/core/context_processors.py

@@ -0,0 +1,14 @@
+from pathlib import Path
+
+_VERSION = None
+
+
+def app_version(request):
+    global _VERSION
+    if _VERSION is None:
+        version_file = Path(__file__).resolve().parent.parent.parent / "VERSION"
+        try:
+            _VERSION = version_file.read_text().strip()
+        except FileNotFoundError:
+            _VERSION = "unknown"
+    return {"APP_VERSION": _VERSION}

app/core/settings.py

@@ -72,6 +72,7 @@ TEMPLATES = [
                 "django.template.context_processors.request",
                 "django.contrib.auth.context_processors.auth",
                 "django.contrib.messages.context_processors.messages",
+                "core.context_processors.app_version",
             ],
         },
     },