WebLN error compatibility issues

While working on an LN React library I noticed that Alby doesn't meet the current WebLN spec by throwing the appropriate pre-defined error messages specified here: https://webln.dev/#/api/errors.

I'm not entirely certain if this project seeks to be webLN compatible, if so I could throw together a PR in an attempt to meet the spec in regards to error handling.

I have also proposed error-handling specific changes to the webln spec that might interest this project here: https://github.com/joule-labs/webln/issues/41

Start by reviewing the WebLN API error definitions at https://webln.dev/#/api/errors and comparing them with Alby's current error handling. Confirm whether WebLN compatibility is in scope; if it is, done means the extension reports the predefined errors required by the specification.

Written by the indexing model from the issue text.