feat: NearbyScreen, configurable clock dashboard, memory optimizations

- Add NearbyScreen: GPS contact list with haversine distance sort,
  type filter (ALL/Chat/Rpt/Room/Snsr), detail view with ping (RTT via
  ACK poll), node scan via advert(), context menu
- Add DashboardConfigScreen: configure up to 3 data fields on the clock
  page (Battery, Temp, Humidity, Pressure, GPS, Altitude, Lux, CO2,
  Contacts); entered via long-press ENTER on clock page
- Rework HP_CLOCK layout: full-screen clock (size 2 at y=0), date at
  y=19, separator at y=28, three data field rows at y=31/41/51;
  hide node name/battery indicator on clock page
- Persist dashboard_fields[3] in NodePrefs and DataStore
- Add isAckPending() to MyMesh for NearbyScreen ping detection
- Wire NearbyScreen into ToolsScreen and UITask
- Reduce NearbyScreen entry buffer from MAX_CONTACTS(100) to 32,
  saving ~3.3 KB RAM
- Switch haversine/bearing math from double to float (sinf/cosf/atan2f),
  eliminating double libm and saving ~5-10 KB flash

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.h

@@ -63,6 +63,8 @@ class UITask : public AbstractUITask {
   UIScreen* tools_screen;
   UIScreen* ringtone_edit;
   UIScreen* bot_screen;
+  UIScreen* nearby_screen;
+  UIScreen* dashboard_config;
   UIScreen* curr;
 
   void userLedHandler();
@@ -98,6 +100,8 @@ public:
   void gotoToolsScreen();
   void gotoRingtoneEditor();
   void gotoBotScreen();
+  void gotoNearbyScreen();
+  void gotoDashboardConfig();
   void playMelody(const char* melody);
   void stopMelody();
   bool isMelodyPlaying();