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/data/keys.toml

@@ -488,8 +488,9 @@ id = "settings"
 title = "Settings"
 rows = [
     ["; .", "up, down"],
-    ["Enter", "edit, or open the page"],
+    ["Enter", "open the group or the page, or edit"],
     [", /", "change a switch or a slider"],
+    ["`", "back to the groups"],
 ]
 
 [[scope]]