M2 step 5: GNSS App, with the Position and Sky views

Position: the Fix line (or how long it has been searching), latitude and
longitude in decimal degrees or degrees-minutes-seconds (Settings ->
Coordinates), the Maidenhead locator, altitude, speed and course, HDOP
and UTC. Sky: the satellites by azimuth and elevation, coloured by
constellation, filled when used in the Fix, with used/in-view counts.
Tab switches. lib/gnss/geo_format holds the formatting, the locator and
the sky projection, host-tested (6 tests; locators checked against
FN31pr and JN58td).

Verified on the device by a window: 3D Fix from GPS, GLONASS, Galileo
and BeiDou.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/gnss/src/geo_format.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <string>
+
+namespace roro::gnss {
+
+// "50.86920° N": five decimals, about a metre.
+std::string formatDecimal(double degrees, bool latitude);
+// "50° 52' 09.1\" N" (Settings → Coordinates, Q64).
+std::string formatDms(double degrees, bool latitude);
+// The 6-character Maidenhead locator ("JO20ef"), as radio amateurs give their square.
+std::string maidenhead(double latitude, double longitude);
+
+// Where a satellite goes on the Sky view: the zenith in the centre, the horizon on the circle,
+// north up and east right (as seen looking at the sky from above, like a map).
+struct SkyPoint {
+    int x, y;
+};
+SkyPoint skyPosition(int azimuthDeg, int elevationDeg, int cx, int cy, int radius);
+
+}  // namespace roro::gnss