feat: Add LandVerpachtung to Django admin interface

- Register LandVerpachtung model in admin for easy production verification
- Add comprehensive list display with status, dates, and relationships
- Include colored status display and proper fieldsets
- Enables verification of Verpachtung functionality in production

app/stiftung/admin.py

@@ -7,7 +7,7 @@ from django.utils.safestring import mark_safe
 from . import models
 from .models import (AppConfiguration, AuditLog, BackupJob, BankTransaction,
                      CSVImport, Destinataer, DestinataerUnterstuetzung,
-                     DokumentLink, Foerderung, Land, Paechter, Person,
+                     DokumentLink, Foerderung, Land, LandVerpachtung, Paechter, Person,
                      Rentmeister, StiftungsKonto, UnterstuetzungWiederkehrend,
                      Verwaltungskosten)
 
@@ -304,6 +304,59 @@ class LandAdmin(admin.ModelAdmin):
     verpachtungsgrad_berechnet.short_description = "Verpachtungsgrad"
 
 
+@admin.register(LandVerpachtung)
+class LandVerpachtungAdmin(admin.ModelAdmin):
+    list_display = [
+        "land",
+        "paechter",
+        "pachtpreis_qm",
+        "laufzeit_von",
+        "laufzeit_bis",
+        "status_display",
+        "erstellt_am",
+    ]
+    list_filter = ["status", "laufzeit_von", "laufzeit_bis", "erstellt_am"]
+    search_fields = ["land__lfd_nr", "land__gemeinde", "paechter__vorname", "paechter__nachname"]
+    ordering = ["-erstellt_am"]
+    readonly_fields = ["id", "erstellt_am", "aktualisiert_am"]
+
+    fieldsets = (
+        ("Verpachtungsdetails", {
+            "fields": ("land", "paechter", "pachtpreis_qm", "status")
+        }),
+        ("Laufzeit", {
+            "fields": ("laufzeit_von", "laufzeit_bis", "kuendigungsfrist_monate")
+        }),
+        ("Finanziell", {
+            "fields": ("kaution", "indexierung", "zahlungsintervall")
+        }),
+        ("Zusatzinformationen", {
+            "fields": ("notizen", "besondere_vereinbarungen"),
+            "classes": ("collapse",)
+        }),
+        ("System", {
+            "fields": ("id", "erstellt_am", "aktualisiert_am"),
+            "classes": ("collapse",)
+        }),
+    )
+
+    def status_display(self, obj):
+        colors = {
+            'aktiv': 'green',
+            'beendet': 'red',
+            'geplant': 'orange',
+            'gekündigt': 'red'
+        }
+        color = colors.get(obj.status, 'black')
+        return format_html(
+            '<span style="color: {}; font-weight: bold;">{}</span>',
+            color,
+            obj.get_status_display()
+        )
+
+    status_display.short_description = "Status"
+
+
 @admin.register(DokumentLink)
 class DokumentLinkAdmin(admin.ModelAdmin):
     list_display = ["titel", "kontext", "paperless_document_id"]