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/clock_screen/clock_screen.md

@@ -6,7 +6,7 @@
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./clk_scr_1_oled.png) | ![](./clk_scr_1_eink.png) |
+| ![](./overview_oled.png) | ![](./overview_eink.png) |
 
 A full-screen clock page on the home screen. Shows the current time and date, with up to three configurable data fields below.
 
@@ -27,7 +27,7 @@ If no time source is available, the screen shows _"! No time sync"_ with a hint
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./clk_scr_2_oled.png) | ![](./clk_scr_2_eink.png) |
+| ![](./fields_oled.png) | ![](./fields_eink.png) |
 
 Up to three data fields are shown below the date separator. Each field displays a label and a value on the same line.
 
@@ -52,4 +52,10 @@ Sensor fields show `--` when the sensor is not connected or has no data.
 
 ### Configuring fields
 
+|           OLED            |           E-Ink           |
+| :-----------------------: | :-----------------------: |
+| ![](./config_oled.png) | ![](./config_eink.png) |
+
+<!-- screenshot pending: Dashboard Config — three field slots cycled with LEFT/RIGHT -->
+
 **Hold Enter** (or press the **Context menu** key) on the Clock page to open the Dashboard Config screen, where each of the three field slots can be cycled with **LEFT/RIGHT**.