Add management command to clear diagram cache

Usage:
  python manage.py clear_diagram_cache
  python manage.py clear_diagram_cache --type plantuml

abschnitte/management/commands/clear_diagram_cache.py

@@ -0,0 +1,23 @@
+from django.core.management.base import BaseCommand
+from diagramm_proxy.diagram_cache import clear_cache
+
+
+class Command(BaseCommand):
+    help = 'Clear cached diagrams'
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            '--type',
+            type=str,
+            help='Diagram type to clear (e.g., plantuml, mermaid)',
+        )
+
+    def handle(self, *args, **options):
+        diagram_type = options.get('type')
+        if diagram_type:
+            self.stdout.write(f'Clearing cache for {diagram_type}...')
+            clear_cache(diagram_type)
+        else:
+            self.stdout.write('Clearing all diagram caches...')
+            clear_cache()
+        self.stdout.write(self.style.SUCCESS('Cache cleared successfully'))