feature: app-store: surface errors to GUI

[nick1udwig]

Is your feature request related to a problem? Please describe.
When errors occur, user is not informed on GUI, e.g.:
https://github.com/kinode-dao/kinode/blob/281c481377e36764dde7d1e25cc0980ab63cc369/kinode/packages/app_store/downloads/src/lib.rs#L136-L143

Describe the solution you'd like
We need to inform the user an error has occurred. There are errors of two classes:

1. Should never happen; these should tell user to inform us
2. Can be remedied with user action (e.g., imagine a node goes down just as a user clicks to download an app from it). Should be user-facing: what happened and what user can do to try to fix it

[nick1udwig]

FYI @bitful-pannul

[nick1udwig]

We need this before v0.10.0 is merged to main. We can use the difference between old & new nodes (app_store -> app-store) to test

[nick1udwig]

@bitful-pannul does #599 resolve this issue or is there more work to be done here? Ideally any error that is encountered can be surfaced