fix(myTischtennis): improve error handling for Playwright login and account verification

- Enhanced error handling in MyTischtennisClient and MyTischtennisService to provide clearer feedback when browser executables are missing.
- Updated responses to include specific error messages and status codes, improving user guidance for setup requirements.
- Refactored MyTischtennisDialog and MyTischtennisAccount components to handle API response errors more effectively, ensuring robust login and account management processes.

frontend/src/components/MyTischtennisDialog.vue

@@ -170,9 +170,14 @@ export default {
       this.error = null;
       this.saving = true;
       try {
-        await apiClient.post('/mytischtennis/verify', {
+        const response = await apiClient.post('/mytischtennis/verify', {
           password: this.formData.password
         });
+        if (response.status >= 400 || response?.data?.success === false) {
+          const requestError = new Error('myTischtennis verify failed');
+          requestError.response = response;
+          throw requestError;
+        }
         this.$emit('logged-in');
       } catch (error) {
         console.error('Fehler beim Login:', error);
@@ -203,7 +208,12 @@ export default {
           payload.userPassword = this.formData.userPassword;
         }
         
-        await apiClient.post('/mytischtennis/account', payload);
+        const response = await apiClient.post('/mytischtennis/account', payload);
+        if (response.status >= 400 || response?.data?.success === false) {
+          const requestError = new Error('myTischtennis account save failed');
+          requestError.response = response;
+          throw requestError;
+        }
         this.$emit('saved');
       } catch (error) {
         console.error('Fehler beim Speichern:', error);

frontend/src/views/MyTischtennisAccount.vue

@@ -233,7 +233,12 @@ export default {
       };
       try {
         // 1-Klick-Re-Login: zuerst gespeicherte Session/Passwort serverseitig verwenden
-        await apiClient.post('/mytischtennis/verify', {});
+        const response = await apiClient.post('/mytischtennis/verify', {});
+        if (response.status >= 400 || response?.data?.success === false) {
+          const requestError = new Error('myTischtennis verify failed');
+          requestError.response = response;
+          throw requestError;
+        }
         await this.loadAccount();
         this.loginFeedback = {
           type: 'success',