refactor: one copy of shared logic and widgets; GPS is asked for, not switched on silently

Duplicates found between the L1 and L2 frontends, and inside the L2 one:
- geo::fmtLocShare / fmtLatLon / turnDeg / isAhead (GeoUtils.h): the [LOC]
  text was built in five places, the turn angle and its "ahead" threshold in
  both navigations, coordinates by hand in nine. Tested.
- LiveShareEngine::setEnabled: live share was switched in three places.
- L1 waypoint share uses WaypointModel::shareText; Trail's "Share my pos"
  goes through UITask::quickShareMyLocation, so it now sends to a running
  live-share session as the home Map page does.
- L2 Widgets.h: switchCreate (one switch size, was four), switchRow with a
  state and callback (16 hand-wired copies), switchRowOpens (Bluetooth, WiFi,
  GPS), primaryButton (one height for Save / Measure / New area / Update).

GPS: with it off, starting the trail, live share or track back, sharing or
marking a position, or centring the map asks first ("GPS is off") on both
L1 and L2; Cancel leaves it undone. A share or a mark waits for a fresh fix
(a switched-off module may still report its last one), which also fixes the
L1 "Share my pos" sending a stale position. SOS still turns the GPS on itself.

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

examples/companion_radio/ui-lvgl/QuickPanel.h

@@ -371,15 +371,18 @@ void UITask::quickPanelTile(int t, bool hold) {
 #endif
       break;
     case T_TRAIL:
-      _core->trail.setActive(!_core->trail.isActive());
-      if (_core->trail.isActive()) ensureGps();   // turns GPS on, or says it's waiting
-      break;
-    case T_SHARE:
+    case T_SHARE: {
       if (!_prefs) break;
-      _prefs->loc_share_enabled = !_prefs->loc_share_enabled;
-      if (_prefs->loc_share_enabled) { _core->live_share.restartSession(); ensureGps(); }
-      prefsSave();
+      const bool on = t == T_TRAIL ? _core->trail.isActive() : _prefs->loc_share_enabled;
+      if (!on && _core->gpsAvailable() && !_core->gpsEnabled()) {   // "GPS is off", over the screen
+        quickPanelClose(false);
+        gpsAsked(t == T_TRAIL ? GA_TRAIL : GA_SHARE);
+        return;
+      }
+      if (t == T_TRAIL) _core->trail.setActive(!on);
+      else { _core->live_share.setEnabled(!on); prefsSave(); }
       break;
+    }
   }
   refreshStatusBar();
   quickPanelRefresh();