✨ Enhance NATS configuration and error handling. Introduce stream limits and consumer rules in configuration files. Refactor message processing to handle permanent errors. Update README and development configuration to reflect changes. Add tests for new error handling mechanisms.

internal/app/errors.go

@@ -0,0 +1,39 @@
+package app
+
+import "errors"
+
+// PermanentError indicates a failure that should not be retried.
+type PermanentError struct {
+	err error
+}
+
+// Error implements the error interface.
+func (e *PermanentError) Error() string {
+	if e == nil || e.err == nil {
+		return ""
+	}
+	return e.err.Error()
+}
+
+// Unwrap allows errors.Unwrap/Is/As to inspect the underlying error.
+func (e *PermanentError) Unwrap() error {
+	if e == nil {
+		return nil
+	}
+	return e.err
+}
+
+// Permanent wraps err to mark it as non-retriable.
+func Permanent(err error) error {
+	if err == nil {
+		return nil
+	}
+	return &PermanentError{err: err}
+}
+
+// IsPermanent reports whether the error or any wrapped error is permanent.
+func IsPermanent(err error) bool {
+	var target *PermanentError
+	return errors.As(err, &target)
+}
+