feat: Add termination functionality for rental agreements

- Introduced new entity `CKuendigung` for managing terminations.
- Added fields for termination details including date, reason, type, and status.
- Implemented backend service to initiate terminations from rental agreements.
- Created frontend handler for termination actions with confirmation dialog.
- Updated metadata and layouts for `CKuendigung` to support new functionality.
- Added internationalization support for English and German languages.
- Enhanced existing entities to establish relationships with terminations.

custom/Espo/Custom/Controllers/CVmhMietverhltnis.php

@@ -42,4 +42,22 @@ class CVmhMietverhltnis extends \Espo\Core\Templates\Controllers\BasePlus
         
         return $result;
     }
+    
+    /**
+     * POST Action: Initiate termination from Mietverhältnis
+     */
+    public function postActionInitiateTermination(Request $request): array
+    {
+        $data = $request->getParsedBody();
+        
+        $id = $data->id ?? null;
+        if (!$id) {
+            throw new BadRequest('No Mietverhältnis ID provided');
+        }
+        
+        $service = $this->getRecordService();
+        $result = $service->initiateTermination($id);
+        
+        return $result;
+    }
 }