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>

docs/solo_features/settings_screen/settings_screen.md

@@ -6,7 +6,7 @@
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./set_scr_1_oled.png) | ![](./set_scr_1_eink.png) |
+| ![](./overview_oled.png) | ![](./overview_eink.png) |
 
 All settings are saved to flash and restored on next boot. Settings are organised into collapsible sections. Press **Enter** on a section header to expand or collapse it — all sections start collapsed for faster navigation. Press **LEFT/RIGHT** to change a value, or **Enter** for toggle items.
 
@@ -50,7 +50,7 @@ Melody 1 and Melody 2 are custom sequences editable in **Tools › Ringtone Edit
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./set_scr_2_oled.png) | ![](./set_scr_2_eink.png) |
+| ![](./homepages_oled.png) | ![](./homepages_eink.png) |
 
 Lists all available home screen pages. For each entry:
 
@@ -74,6 +74,12 @@ Lists all available home screen pages. For each entry:
 | Pwr save  | ON / OFF   | **Battery saver.** Hardware duty-cycle receive: the SX126x cycles RX↔sleep on its own and wakes on a preamble, cutting average RX current. Trades a little receive latency; leave OFF for lowest-latency reception. Requires an SX126x radio (otherwise stays on continuous RX). **Forced off (shown as `--`) while the repeater is on** — a repeater must listen continuously; your setting is restored when the repeater is switched off. |
 | Auto pwr  | ON / OFF   | **Adaptive Power Control.** Lowers actual TX power on strong links to save energy, ramping back up — to the **TX Pwr** ceiling — on weak or lost links. Link quality comes from direct-message ACK SNR and, for channel messages (no ACK), from hearing a repeater rebroadcast your packet. The radio page / name bar shows the live power. Default OFF (fixed TX power). **Suppressed (shown as `--`) while the repeater is on** — a repeater holds full TX power for consistent relay reach; your setting is restored when the repeater is switched off. |
 
+|           OLED            |           E-Ink           |
+| :-----------------------: | :-----------------------: |
+| ![](./radio_oled.png) | ![](./radio_eink.png) |
+
+<!-- screenshot pending: Radio — preset popup (pick/save/delete) and/or the digit-by-digit frequency editor -->
+
 The **repeater** mode and its flood filters live on their own screen — see **Tools › Repeater**.
 
 ---