add friendly error messages to fallback auth

            <Stack direction="column" gap={1} sx={{ mt: 1 }}>

              {errors.map(({ code, meta }) => {

                switch (code) {

                  case "failed_to_find_user":

                    return (

                      <Alert key={code} severity="error">

                        <b>Failed to find user</b>

                        <br />

                        {/* TODO: remove hardcoded instance */}

                        Your instance may not be federated with grants.cafe,

                        unable to verify.

                      </Alert>

                    );

                  case "no_mentions":

                    return (

                      <Alert key={code} severity="info">

                        <b>No mentions, yet</b>

                        <br />

                        Make sure you make a post that the account can see

                      </Alert>

                    );

                  case "message_content_invalid":

                    return (

                      <Alert key={code} severity="warning">

                        <b>Message content isn&apos;t the expected</b> Make sure

                        the post content is what is below

                      </Alert>

                    );

                  case "no_polyfill":

                    return (

                      <Alert key={code} severity="error">