Prevent chord backup download while chords are still in process of being read from the device

[jdestgermain]

From Ekagu on Discord:

The managers 'backup everything' button didn't back up the chords, only the layout and settings.

Cause:
It's reproducible by backing up everything while the chords are being read:
open a new browser window (tested in Edge), or clear the manager's site data
open https://manager.charachorder.com/config/layout/
perform the next steps 'quickly', before the Reading chords progress bar finishes
connect
click on the top right local backup button (clock icon)
click on the button 'download everything'

observed:
a backup file is downloaded, with all three sections: chords, layout, and settings
but the chords section is empty.

expected:
disable (red bg color?) both the 'Chords' button (in the individual backups section) and the 'Download Everything' button
change the text: 'Wait... reading chords' on the buttons.
maybe:
show a popup message when the buttons are pressed
and/or if either button is pressed, flash (red?) both the buttons and the reading chords progress bar at the bottom of the page

If it's better to not back up anything until the chords have been read.
Replace the whole local backup popup with the message: Wait... reading chords

enable the buttons and change back the text/color when the chords have been read.

The issue was discovered like this:
before updating to the new firmware
read the update docs that suggested making a backup
connected to the manager
clicked on 'download everything'
clicked on the 'bootloader' button, and noticed that it made an automatic backup
after updating, opened the download folder and noticed a size difference between the backup files
manual backup: 2 KB (chords section [] is empty)
automatic backup: 37 KB

the layout and settings sections are populated as expected in both the manual and automatic backups.