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

src/services/gnss_service.h

@@ -35,6 +35,7 @@ class GnssService : public Service {
     bool on() const { return active_; }
     bool receiving(uint32_t nowMs) const { return active_ && lastLineMs_ && nowMs - lastLineMs_ < kSilentAfterMs; }
     const gnss::GnssState& state() const { return parser_.state(); }
+    uint32_t onSinceMs() const { return openedMs_; }  // when the receiver was last woken
 
     // Debug aids (Q68): raw sentences to the console, a status report, and sending a command
     // ("PCAS10,0" becomes "$PCAS10,0*1C\r\n").