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/AdminScreen.h

@@ -309,10 +309,7 @@ void UITask::adminValuePopup() {
   if (f->kind == admin::K_ONOFF) {
     lv_obj_t* r = centerRow(panel);
     label(r, "Off", THEME_FONT_BODY, theme::TEXT_MUTED);
-    lv_obj_t* sw = lv_switch_create(r);
-    lv_obj_set_size(sw, 56, 28);
-    if (S.value != 0) lv_obj_add_state(sw, LV_STATE_CHECKED);
-    lv_obj_add_event_cb(sw, onAdminValue, LV_EVENT_VALUE_CHANGED, (void*)(uintptr_t)V_TOGGLE);
+    switchCreate(r, S.value != 0, onAdminValue, (void*)(uintptr_t)V_TOGGLE);
     label(r, "On", THEME_FONT_BODY, theme::TEXT_MUTED);
   } else if (f->kind == admin::K_NUMBER) {
     lv_obj_t* r = centerRow(panel);