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

scripts/sd_put.py

@@ -2,7 +2,7 @@
 """Copies a file to the Cardputer's SD card over the USB serial console (the `sd put` command).
 
 Usage: scripts/sd_put.sh <file> [card path]
-The card path defaults to /updates/<file name>, where Settings > Firmware finds Update Files.
+The card path defaults to /updates/<file name>, where Settings > System > Firmware finds Update Files.
 The device acknowledges each chunk once it's on the card, checks the SHA-256 of the whole file,
 and only then renames <card path>.part to <card path>.
 """