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/DataStore.cpp

@@ -266,6 +266,9 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
                   file.read((uint8_t *)&_prefs.buzzer_auto, sizeof(_prefs.buzzer_auto));
                   if (file.available()) {
                     file.read((uint8_t *)_prefs.dm_notif, sizeof(_prefs.dm_notif));
+                    if (file.available()) {
+                      file.read((uint8_t *)_prefs.dashboard_fields, sizeof(_prefs.dashboard_fields));
+                    }
                   }
                 }
               }
@@ -338,6 +341,7 @@ void DataStore::savePrefs(const NodePrefs& _prefs, double node_lat, double node_
     file.write((uint8_t *)&_prefs.clock_hide_seconds, sizeof(_prefs.clock_hide_seconds));
     file.write((uint8_t *)&_prefs.buzzer_auto, sizeof(_prefs.buzzer_auto));
     file.write((uint8_t *)_prefs.dm_notif, sizeof(_prefs.dm_notif));
+    file.write((uint8_t *)_prefs.dashboard_fields, sizeof(_prefs.dashboard_fields));
 
     file.close();
   }