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/GeoUtils.h

@@ -61,6 +61,19 @@ static inline void fmtDist(char* buf, int n, float km, bool imperial) {
   }
 }
 
+// Compact age tag for a timestamp, e.g. "12s" / "5m" / "3h" / "2d" — sized to
+// sit inline after a name (unlike a full "X ago" sentence). Empty string for
+// an unknown (0) or future timestamp. Takes `now` rather than reading the RTC
+// itself, so this stays a pure function like the rest of this file.
+static inline void fmtAgeShort(char* buf, int n, uint32_t now, uint32_t lastmod) {
+  if (lastmod == 0 || now < lastmod) { buf[0] = '\0'; return; }
+  uint32_t age = now - lastmod;
+  if      (age < 60)    snprintf(buf, n, "%us", (unsigned)age);
+  else if (age < 3600)  snprintf(buf, n, "%um", (unsigned)(age / 60));
+  else if (age < 86400) snprintf(buf, n, "%uh", (unsigned)(age / 3600));
+  else                  snprintf(buf, n, "%ud", (unsigned)(age / 86400));
+}
+
 // Tag marking a shared waypoint inside a message: "[WAY]<lat>,<lon> <label>".
 // A plain {loc} expansion ("<lat>,<lon>") parses too — the tag just adds intent
 // and a label, and keeps the text readable on apps/firmware that don't know it.
@@ -109,4 +122,23 @@ static inline bool parseLatLon(const char* text, int32_t& lat_1e6, int32_t& lon_
   return false;
 }
 
+// Tag marking a live position share inside a message: "[LOC]<lat>,<lon>".
+// Distinct from WAYPOINT_MSG_TAG: a waypoint is a static point-of-interest to
+// save, whereas this announces the *sender's own* current position so the
+// receiver can update its bearing/track on that node. Both reuse parseLatLon
+// for the coordinate, and both stay readable on firmware/apps that don't know
+// the tag (it just looks like a coordinate).
+#define LOCATION_MSG_TAG "[LOC]"
+
+// True if `text` carries a LOCATION_MSG_TAG share; fills lat/lon (1e6-scaled)
+// from the coordinate that follows it. Returns false for plain text, for a
+// bare coordinate, or for a [WAY] share — only an explicit [LOC] tag counts,
+// so ordinary messages that happen to contain digits don't move anyone's pin.
+static inline bool parseLocShare(const char* text, int32_t& lat_1e6, int32_t& lon_1e6) {
+  if (!text) return false;
+  const char* tag = strstr(text, LOCATION_MSG_TAG);
+  if (!tag) return false;
+  return parseLatLon(tag + strlen(LOCATION_MSG_TAG), lat_1e6, lon_1e6);
+}
+
 }  // namespace geo