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/dev/build/how-an-update-works/ways-in.svg

@@ -21,7 +21,7 @@
     <rect class="wi-panel" x="288" y="176" width="200" height="88" rx="8"/>
     <text x="302" y="200" font-size="12" font-weight="600">SD card</text>
     <text x="302" y="219" font-size="11">/updates/*.ota</text>
-    <text x="302" y="238" font-size="11" class="wi-dim">Settings → Firmware,</text>
+    <text x="302" y="238" font-size="11" class="wi-dim">Settings → System → Firmware,</text>
     <text x="302" y="254" font-size="11" class="wi-dim">or install &lt;path&gt;</text>
 
     <rect class="wi-hot" x="536" y="32" width="208" height="158" rx="8"/>