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/templates/downloads.html

@@ -11,7 +11,7 @@
   </header>
 
   <div class="prose">
-    <p>Each release has a <strong>signed update file</strong> (<code>.ota</code>: copy it to <code>/updates</code> on the SD card and install it from Settings → Firmware or the Storage App, or push it over Wi-Fi), a <strong>factory image</strong> (<code>-factory.bin</code>, the whole flash at offset 0 for a first install over USB), the <strong>symbols</strong> (<code>.elf.gz</code>, to decode a crash report) and <code>SHA256SUMS</code>.</p>
+    <p>Each release has a <strong>signed update file</strong> (<code>.ota</code>: copy it to <code>/updates</code> on the SD card and install it from Settings → System → Firmware or the Storage App, or push it over Wi-Fi), a <strong>factory image</strong> (<code>-factory.bin</code>, the whole flash at offset 0 for a first install over USB), the <strong>symbols</strong> (<code>.elf.gz</code>, to decode a crash report) and <code>SHA256SUMS</code>.</p>
   </div>
 
   {% if releases %}