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/UITask.h

@@ -404,7 +404,12 @@ public:
   void pinPopup(bool channel, uint8_t ch_idx, const uint8_t* pub_key);
   void pinTo(int slot);
   void setGps(bool on);
-  bool ensureGps();   // true with a fix; else turns GPS on / says it's waiting
+  // What needs the GPS while it's off: asked first ("GPS is off"), then done
+  // once it's turned on (GpsScreen.h).
+  enum GpsAsk : uint8_t { GA_TRAIL, GA_SHARE, GA_TRACKBACK, GA_CENTRE, GA_FIX };
+  bool gpsAsked(GpsAsk what);    // true: it was off, the question is up
+  bool ensureGps(GpsAsk what);   // true with a fix; else asks, or says it's waiting
+  void gpsAskDone(GpsAsk what);
 
   // Kept for main.cpp's sim hooks (ui-new API).
   void openContactDM(const ContactInfo& ci) { openDM(ci.id.pub_key); }