feat: initial backend scaffolding

migrating away from convex

Co-authored-by: Ona <no-reply@ona.com>

apps/backend/internal/auth/err.go

@@ -0,0 +1,19 @@
+package auth
+
+import "fmt"
+
+type InvalidAccessTokenError struct {
+	err error
+}
+
+func newInvalidAccessTokenError(err error) *InvalidAccessTokenError {
+	return &InvalidAccessTokenError{err}
+}
+
+func (e *InvalidAccessTokenError) Error() string {
+	return fmt.Sprintf("invalid access token: %v", e.err)
+}
+
+func (e *InvalidAccessTokenError) Unwrap() error {
+	return e.err
+}