feat: improve error handling with proper HTTP status codes

src/main/java/com/litoralregas/openvpn/common/ApiExceptionHandler.java

@@ -15,9 +15,22 @@ public class ApiExceptionHandler {
         return Map.of("error", exception.getMessage());
     }
 
+    @ResponseStatus(HttpStatus.CONFLICT)
+    @ExceptionHandler(IllegalStateException.class)
+    public Map<String, String> handleIllegalState(IllegalStateException exception) {
+        return Map.of("error", exception.getMessage());
+    }
+
     @ResponseStatus(HttpStatus.BAD_REQUEST)
     @ExceptionHandler(MethodArgumentNotValidException.class)
     public Map<String, String> handleValidation(MethodArgumentNotValidException exception) {
         return Map.of("error", "Validation failed");
     }
+
+    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
+    @ExceptionHandler(Exception.class)
+    public Map<String, String> handleGeneric(Exception exception) {
+        return Map.of("error", "Internal server error");
+    }
+
 }