feat(units): global metric/imperial setting for all distance displays

Add a single "Units" choice (Settings › System: Metric / Imperial) that
governs every distance and speed shown in Tools — Nearby Nodes, the Trail
views, and the navigate-to-point screen.

- NodePrefs: units_imperial (global) + trail_show_pace (Trail readout mode),
  schema bumped 0xC0DE0005 → 0006. The old combined trail_units_idx is kept
  for file-layout stability but no longer drives anything; upgraders default
  to metric + speed.
- geo::fmtDist gains an imperial mode (ft below ~1000 ft, then miles).
- NavView / Nearby / Trail (waypoint list, Summary distance, List deltas,
  map scale-bar label) all format through the global preference.
- Trail's action-menu "Units" row becomes a Speed/Pace readout toggle; the
  km-vs-mi unit now follows the global setting instead of being one of four
  combined options.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/NearbyScreen.h

@@ -85,6 +85,12 @@ class NearbyScreen : public UIScreen {
   // Geographic helpers live in GeoUtils.h (geo::) — shared with Waypoints /
   // trail course-over-ground. Call sites use geo:: directly.
 
+  // Global metric/imperial preference for distance display.
+  bool useImperial() const {
+    NodePrefs* p = _task ? _task->getNodePrefs() : nullptr;
+    return p && p->units_imperial;
+  }
+
   static void fmtAge(char* buf, int n, uint32_t lastmod) {
     uint32_t now = rtc_clock.getCurrentTime();
     if (now < lastmod || lastmod == 0) { snprintf(buf, n, "unknown"); return; }
@@ -366,7 +372,7 @@ class NearbyScreen : public UIScreen {
 
     if (e.dist_km >= 0.0f) {
       char dist[12];
-      geo::fmtDist(dist, sizeof(dist), e.dist_km);
+      geo::fmtDist(dist, sizeof(dist), e.dist_km, useImperial());
       int az = geo::bearingDeg(_own_lat, _own_lon, e.lat_e6, e.lon_e6);
       snprintf(buf, sizeof(buf), "Dist: %s %s", dist, geo::bearingCardinal(az));
     } else {
@@ -582,7 +588,7 @@ public:
       const Entry& e = _entries[_sel];
       int cog; bool cogv = _task->currentCourse(cog);
       navview::draw(display, _own_gps, _own_lat, _own_lon,
-                    e.lat_e6, e.lon_e6, e.name, cogv, cog);
+                    e.lat_e6, e.lon_e6, e.name, cogv, cog, useImperial());
       return 1000;
     }
 
@@ -622,7 +628,7 @@ public:
 
         display.setColor(sel ? DisplayDriver::DARK : DisplayDriver::LIGHT);
         char dist[10];
-        if (e.dist_km >= 0.0f) geo::fmtDist(dist, sizeof(dist), e.dist_km);
+        if (e.dist_km >= 0.0f) geo::fmtDist(dist, sizeof(dist), e.dist_km, useImperial());
         else                   strncpy(dist, "?GPS", sizeof(dist));
         display.setCursor(dist_col, y);
         display.print(dist);