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/NavView.h

@@ -18,7 +18,8 @@ inline void draw(DisplayDriver& d,
                  bool own_valid, int32_t own_lat, int32_t own_lon,
                  int32_t tgt_lat, int32_t tgt_lon,
                  const char* label,
-                 bool cog_valid, int cog_deg) {
+                 bool cog_valid, int cog_deg,
+                 bool imperial) {
   const int cx  = d.width() / 2;
   const int hdr = d.headerH();
 
@@ -40,7 +41,7 @@ inline void draw(DisplayDriver& d,
   int   to_deg = geo::bearingDeg(own_lat, own_lon, tgt_lat, tgt_lon);
   float dist_km = geo::haversineKm(own_lat, own_lon, tgt_lat, tgt_lon);
   char dist[12];
-  geo::fmtDist(dist, sizeof(dist), dist_km);
+  geo::fmtDist(dist, sizeof(dist), dist_km, imperial);
 
   const int step = d.lineStep();
   int y = hdr + 2;