GNSS App: a Compass, with Places to be led back to and a level

Tab goes on from the Sky to a third view (issue #16): a rose that turns
with the device, the heading, where north came from and how long ago,
the sun on the rose, and a level. m marks where you stand as a Place,
t picks one as the target: an arrowhead on the rose, its distance and
bearing. The sensor's directions were checked by hand on the device.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

lib/core/src/app_keys.h

@@ -134,10 +134,26 @@ inline constexpr KeyHelp kWifiTracker[] = {
 
 // gnss: GNSS
 inline constexpr KeyHelp kGnss[] = {
-    {"Tab", "the position, or the sky"},
+    {"Tab", "position, sky, compass"},
     {"r", "record a Track, or stop it"},
 };
 
+// gnss-compass: GNSS, the compass
+inline constexpr KeyHelp kGnssCompass[] = {
+    {"Tab", "position, sky, compass"},
+    {"m", "mark this place"},
+    {"t", "the target: a place"},
+    {"s", "aimed at the sun: north"},
+    {"r", "record a Track, or stop it"},
+};
+
+// gnss-places: GNSS, the places
+inline constexpr KeyHelp kGnssPlaces[] = {
+    {"; .", "up, down"},
+    {"Enter", "the target"},
+    {"d  Del", "remove the place"},
+};
+
 // gemini: Gemini, a page
 inline constexpr KeyHelp kGemini[] = {
     {"Tab", "the next link"},