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

src/apps/debug_console_page.h

@@ -15,7 +15,7 @@
 
 namespace roro {
 
-// Settings → Debug Console (ADR 0010): the switch, where to connect, and the token, which is shown
+// Settings → System → Debug Console (ADR 0010): the switch, where to connect, and the token, which is shown
 // here and nowhere else. Switching on makes a token if there's none; a new one, or one typed by
 // hand, ends the connection of whoever holds the old one.
 class DebugConsolePage {