feat(companion): live location sharing, Locator geofencing, trail auto-pause

Squash merge of feat/location-beacon-alerts-autopause (v1.21).

Features:
- Live Location Sharing — broadcast position as movement-gated [LOC]
  messages to a channel or contact; live shares show as map pins with
  distance/bearing in Nearby Nodes and a status-bar indicator. [LOC] is
  parsed in DMs, channel messages and room messages; DM shares name the
  sender.
- Locator (geofence) — arm a geofence around a saved waypoint or a person
  (live [LOC] or last-known position), alert on arrive/leave or near/far,
  with an optional homing beeper (gated to arrive/both modes). Arm from
  Tools > Locator, Nearby Nodes, or Waypoints; target picker lists
  favourites first, clearable via a "None" entry. Active target is drawn
  as a flag on the map.
- One active target shared across Locator / Navigate / Map via a single
  resolver (resolvePersonPos / activeTargetPos) that prefers a live
  [LOC] share over the last-advertised GPS fix.
- Follow live contacts — Navigate to a live-sharing contact follows them
  as they move and adds an ETA line; quick-share your own position from
  the Map.
- Map & status-bar upgrades — home mini-map gets a north marker, scale
  tick, and a connected trail line (was disconnected dots); status line
  shows tracked-node count, an arrow + distance to the active Locator/Nav
  target (falling back to the nearest live-tracked contact); GPS fix icon
  in the top status bar, shown only on GPS boards with GPS enabled.
- Trail auto-pause — recording freezes on stops (banking elapsed time,
  breaking the map line across the idle gap) and resumes on movement
  without ending the session.
- Streaming trail simplification — GPS points are simplified in-stream
  via a fixed-corridor (Reumann-Witkam) pass tuned for fidelity: straight
  runs collapse to their endpoints, curves stay bounded to the Min-dist
  tolerance, so the 512-point buffer covers a far longer route than a
  flat point budget would suggest.
- Collapsible Tools (Location / Comms / System sections, fold-in-place
  like Settings) and page-indicator icons on the home carousel.
- Waypoint coordinate editor — add a waypoint by scroll-editing lat/lon
  digit by digit.

Fixes:
- Critical: low-heap hang and contact loss on RAM-tight builds. Halved
  message-history scrollback rings (recovering ~14 KB free heap) and
  made contacts/channels/prefs persistence atomic (temp file + rename),
  so an interrupted save can no longer corrupt or wipe the store.
- Serial.write() bounded so a stalled USB host can't hang the device.
- Nearby Nodes: live [LOC] senders respect the type filter, sort by
  shared position, and the list refreshes so live shares bubble up.
- Map: live contacts are labelled before waypoints.
- GPS status icon hidden when GPS is off in Settings.
- Splash screen no longer truncates a pre-release tag's own dash (e.g.
  v1.21-rc1) when stripping the build's commit-hash suffix.
- Null-guarded the Locator target picker; clamped loc-share channel
  index on load.

Under the hood:
- -Os size optimisation on the e-ink and GAT562 30S solo envs.

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

examples/companion_radio/ui-new/GfxUtils.h

@@ -6,6 +6,7 @@
 
 #include <helpers/ui/DisplayDriver.h>
 #include <stdlib.h>   // abs
+#include "../Trail.h"
 
 namespace gfx {
 
@@ -37,4 +38,25 @@ static inline void drawCircle(DisplayDriver& d, int cx, int cy, int r) {
   }
 }
 
+// Walks a TrailStore and renders it as a connected polyline via drawLine(),
+// breaking the line at each TRAIL_FLAG_SEG_START point (trail paused/
+// restarted) instead of bridging the dead-time gap. Shared by the full Trail
+// map and the Home screen's mini-map preview, which only differ in how they
+// project lat/lon to screen coords and what (if anything) they draw at a
+// break. `project(lat, lon, x, y)` fills the screen coords for one point;
+// `on_break(x_prev_end, y_prev_end, x_new_start, y_new_start)` runs at each
+// break instead of drawLine() — pass a no-op lambda for a silent gap.
+template <typename Project, typename OnBreak>
+static void drawTrail(DisplayDriver& d, TrailStore& tr, Project project, OnBreak on_break) {
+  if (tr.count() == 0) return;
+  int x0, y0; project(tr.at(0).lat_1e6, tr.at(0).lon_1e6, x0, y0);
+  for (int i = 1; i < tr.count(); i++) {
+    const TrailPoint& pt = tr.at(i);
+    int x1, y1; project(pt.lat_1e6, pt.lon_1e6, x1, y1);
+    if (pt.flags & TRAIL_FLAG_SEG_START) on_break(x0, y0, x1, y1);
+    else                                  drawLine(d, x0, y0, x1, y1);
+    x0 = x1; y0 = y1;
+  }
+}
+
 }  // namespace gfx