Add projects

backend/sdk/auth/errors.go

@@ -0,0 +1,13 @@
+package auth
+
+// EmailRequiredError indicates that the calling context must provide an email or alias.
+type EmailRequiredError struct {
+	Prompt string
+}
+
+func (e *EmailRequiredError) Error() string {
+	if e == nil || e.Prompt == "" {
+		return "cliproxy auth: email is required"
+	}
+	return e.Prompt
+}