display proper error when object does not exist

[Johann150]

Summary

Currently, when a user goes to a URL of a note that does not exist, the client will show a generic error and a retry button. This can easily lead users to click on the button repeatedly even though the server is telling the client that the note does not exist.

[Johann150]

I'm not sure if this should better be handled in packages/client/src/pages/note.vue or in the MkError component. There already is an intended facility to pass an error object to MkError so it might make sense to try to detect special error codes or error IDs.

[Johann150]

I think the same can be applied to pages of not existing users, pages etc.