send iOS notifications

there were multiple times where i had wished that there was a way to notify me of some task (e.g. cloning a repository or converting a video with ffmpeg) finishing so that I wouldn't have to constantly keep checking if it finished or not.

it could be something like:
```
/proc/ish/notify "Hello, World!"
```

Start from the proposed `/proc/ish/notify` command and trace how ish exposes proc commands and connects to iOS functionality. Define completion as accepting a message such as “Hello, World!” and delivering it as an iOS notification, then determine the required test coverage.

Written by the indexing model from the issue text.