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/NodePrefs.h

@@ -60,4 +60,5 @@ struct NodePrefs {  // persisted to file
   struct DmNotifEntry { uint8_t prefix[4]; uint8_t state; }; // state: 0=default,1=muted,2=force-on
   static const int DM_NOTIF_TABLE_MAX = 16;
   DmNotifEntry dm_notif[DM_NOTIF_TABLE_MAX]; // 16*5 = 80 bytes
+  uint8_t  dashboard_fields[3]; // 0=None,1=Batt,2=Temp,3=Hum,4=Pres,5=GPS,6=Alt,7=Lux,8=CO2,9=Nodes
 };