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/ToolsScreen.h

@@ -6,7 +6,7 @@ class ToolsScreen : public UIScreen {
   UITask* _task;
   int _sel;
 
-  static const int ITEM_COUNT = 2;
+  static const int ITEM_COUNT = 3;
   static const char* ITEMS[ITEM_COUNT];
 
 public:
@@ -44,8 +44,9 @@ public:
     if (c == KEY_ENTER) {
       if (_sel == 0) { _task->gotoRingtoneEditor(); return true; }
       if (_sel == 1) { _task->gotoBotScreen();      return true; }
+      if (_sel == 2) { _task->gotoNearbyScreen();   return true; }
     }
     return false;
   }
 };
-const char* ToolsScreen::ITEMS[2] = { "Ringtone Editor", "Auto-Reply Bot" };
+const char* ToolsScreen::ITEMS[3] = { "Ringtone Editor", "Auto-Reply Bot", "Nearby Nodes" };