feat(xerrors)!: promote to v1.0.0 — add Unauthorized and PermissionDenied constructors

Add Unauthorized and PermissionDenied convenience constructors to complete the
set of the five most-used error codes (InvalidInput, NotFound, Internal,
Unauthorized, PermissionDenied). All roadmap items from v0.9.0 resolved.
API committed as stable.

xerrors.go

@@ -67,6 +67,18 @@ func Internal(msg string, args ...any) *Err {
 	return New(ErrInternal, fmt.Sprintf(msg, args...))
 }
 
+// Unauthorized creates an Err with [ErrUnauthorized] code.
+// msg is formatted with args using [fmt.Sprintf] rules.
+func Unauthorized(msg string, args ...any) *Err {
+	return New(ErrUnauthorized, fmt.Sprintf(msg, args...))
+}
+
+// PermissionDenied creates an Err with [ErrPermissionDenied] code.
+// msg is formatted with args using [fmt.Sprintf] rules.
+func PermissionDenied(msg string, args ...any) *Err {
+	return New(ErrPermissionDenied, fmt.Sprintf(msg, args...))
+}
+
 // WithContext adds a key-value pair to the error's context fields and returns
 // the receiver for chaining. Calling it multiple times with the same key
 // overwrites the previous value.