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.

client/custom/src/handlers/mietverhaeltnis/termination-action.js

@@ -0,0 +1,70 @@
+define('custom:handlers/mietverhaeltnis/termination-action', [], function () {
+    
+    class TerminationActionHandler {
+        
+        constructor(view) {
+            this.view = view;
+        }
+        
+        /**
+         * Setup-Methode wird automatisch aufgerufen
+         */
+        initInitiateTermination() {
+            // Optional: Button-Logik nach Render
+        }
+        
+        /**
+         * Action-Handler (wird bei Button-Click aufgerufen)
+         */
+        actionInitiateTermination() {
+            console.log('actionInitiateTermination called');
+            const model = this.view.model;
+            
+            // Confirmation Dialog
+            this.view.confirm(
+                this.view.translate('confirmTermination', 'messages', 'CVmhMietverhltnis'),
+                () => {
+                    console.log('Confirmation accepted, initiating termination');
+                    this.initiateTermination(model.id);
+                }
+            );
+        }
+        
+        /**
+         * AJAX Request zum Backend
+         */
+        initiateTermination(mietverhaeltnisId) {
+            Espo.Ui.notify(this.view.translate('pleaseWait', 'messages'));
+            
+            Espo.Ajax.postRequest('CVmhMietverhltnis/action/initiateTermination', {
+                id: mietverhaeltnisId
+            })
+            .then(response => {
+                Espo.Ui.success(
+                    this.view.translate('terminationCreated', 'messages', 'CVmhMietverhltnis')
+                );
+                
+                // Navigation zur erstellten Kündigung
+                this.view.getRouter().navigate(
+                    '#CKuendigung/view/' + response.id, 
+                    {trigger: true}
+                );
+            })
+            .catch(xhr => {
+                console.error('Termination initiation failed:', xhr);
+                
+                let errorMessage = this.view.translate('terminationError', 'messages', 'CVmhMietverhltnis');
+                
+                if (xhr.status === 403) {
+                    errorMessage = this.view.translate('Access denied', 'messages');
+                } else if (xhr.status === 404) {
+                    errorMessage = this.view.translate('Not found', 'messages');
+                }
+                
+                Espo.Ui.error(errorMessage);
+            });
+        }
+    }
+    
+    return TerminationActionHandler;
+});