feat(l2): a turn dial in the navigation bar

An arrow at the target on a round dial whose top is the way you're heading:
turn until it points up. It turns green and the ring doubles when you're
within 12 degrees. The text says how far to turn ("turn right 55") instead of
two bearings to subtract. Standing still there's no course: the arrow greys
out, the top is north and marked red, and the text keeps the bearing.

sim_nav_target() sets a target from the simulator page.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-lvgl/UITask.h

@@ -172,6 +172,7 @@ public:
   void setMapLayer(int i);
   void simMapAt(const char* spec);      // Map tools > Live tiles
   void simCompose(const char* text);    // the open thread's field: this text, keyboard up
+  void simNavTarget(int32_t lat_1e6, int32_t lon_1e6);   // a waypoint as the navigation target
   void simDm();                         // the first chat contact's thread
   void simUnread();                     // read and new messages to open on
   void simSleep(bool on) { if (on) sleep(); else wake(); }