Settings: its rows in five groups

Settings had grown to 21 rows in one list. It opens on five groups (This
device, Display, GNSS and radio, Network, System); Enter opens one, Back
returns to the groups, and Back from the groups leaves Settings.

SettingsMenu holds the groups and which one is open (host-tested: every
setting is in exactly one group). The guide, the how-tos, the README,
the scripts' messages and the firmware's own name the new paths, such as
"Settings > System > Firmware".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

site/content/howto/screenshot.md

@@ -14,5 +14,5 @@ tag = "Screen"
 
 - It needs an SD card.
 - The files are PNGs of 240 by 135 pixels, named by date and time.
-- **It refuses on Settings → Debug Console**, the page that shows the console's token: a picture of it would be a copy of the token.
+- **It refuses on Settings → System → Debug Console**, the page that shows the console's token: a picture of it would be a copy of the token.
 - From the [Shell](/guide/shell/), `screenshot 5` takes the picture five seconds later, for a screen you can't press keys on.