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>

variants/gat562_30s_mesh_kit/platformio.ini

@@ -116,6 +116,11 @@ lib_deps =
 extends = GAT562_30S_Mesh_Kit
 board_build.ldscript = boards/nrf52840_s140_v6_extrafs.ld
 board_upload.maximum_size = 712704
+; Optimise for size, not speed: the nRF52 Arduino core defaults to -Ofast
+; (≈ -O3 + -ffast-math), which bloats flash by ~200 KB on this feature-rich
+; solo build. -Os keeps every feature, fits comfortably, and is actually safer
+; for float (no fast-math reassociation). Speed is irrelevant for the UI/mesh.
+build_unflags = -Ofast
 build_flags =
   ${GAT562_30S_Mesh_Kit.build_flags}
   -I examples/companion_radio/ui-new
@@ -130,6 +135,7 @@ build_flags =
   -D UI_HAS_JOYSTICK_UPDOWN=1
   -D ADVERT_NAME='"@@MAC"'
   -D ENV_INCLUDE_GPS=1
+  -Os
   ; QSPIFLASH disabled: QSPI IO0/IO2 pins (P0.30/P0.28) conflict with joystick LEFT/UP
   ; -D MESH_PACKET_LOGGING=1
   ; -D MESH_DEBUG=1
@@ -148,6 +154,11 @@ lib_deps =
 extends = GAT562_30S_Mesh_Kit
 board_build.ldscript = boards/nrf52840_s140_v6_extrafs.ld
 board_upload.maximum_size = 712704
+; Optimise for size, not speed: the nRF52 Arduino core defaults to -Ofast
+; (≈ -O3 + -ffast-math), which bloats flash by ~200 KB on this feature-rich
+; solo build. -Os keeps every feature, fits comfortably, and is actually safer
+; for float (no fast-math reassociation). Speed is irrelevant for the UI/mesh.
+build_unflags = -Ofast
 build_flags =
   ${GAT562_30S_Mesh_Kit.build_flags}
   -I examples/companion_radio/ui-new
@@ -164,6 +175,7 @@ build_flags =
   -D ENV_INCLUDE_GPS=1
   -D DUAL_SERIAL=1
   -D ENABLE_SCREENSHOT
+  -Os
   ; QSPIFLASH disabled: QSPI IO0/IO2 pins (P0.30/P0.28) conflict with joystick LEFT/UP
   ; -D MESH_PACKET_LOGGING=1
   ; -D MESH_DEBUG=1