web ide: confusing interface when sending files.

### Affected hardware version

Bangle 2

### Your firmware version

2v18

### The bug

I'm uploading ~6MB file to watch using https://www.espruino.com/ide/# . It would be nice if the ide would tell me
what the available space on the watch is.

For 6MB files, upload ends with

Uncaught Error: Unable to find or create file
at line 1 col 159
...yCiB9Cn0tMSAgICA="),6645888);print(">>",">")

(which is quite easy to miss, because it only appears in messages window).

I tried uploading 4MB file, somehow the "uploading" window disappeared, but it seems that upload is continuing. It took 30 minutes so far. If I attempted to run the code now, I guess I'd end up with corrupted file.

### Installed apps

_No response_