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/apps/gnss_app.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "app.h"
+#include "services/gnss_service.h"
+#include "settings.h"
+
+namespace roro {
+
+// GNSS (see docs/milestones/M2.md, Q59): the Position view, and the Sky view with every satellite
+// in view placed by direction and elevation. Tab switches between them.
+class GnssApp : public App {
+   public:
+    GnssApp(GnssService& gnss, const Settings& settings) : gnss_(gnss), settings_(settings) {}
+    void onEnter() override { requestRedraw(); }
+    bool onKey(const KeyEvent& e) override;
+    void update(uint32_t nowMs) override;
+    void draw(Canvas& c) override;
+
+   private:
+    void drawPosition(Canvas& c);
+    void drawSky(Canvas& c);
+
+    GnssService& gnss_;
+    const Settings& settings_;
+    bool sky_ = false;
+    uint32_t lastDrawMs_ = 0;
+};
+
+}  // namespace roro