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/message_screen/message_screen.md

@@ -6,7 +6,7 @@
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_1_oled.png) | ![](./mes_scr_1_eink.png) |
+| ![](./overview_oled.png) | ![](./overview_eink.png) |
 
 The Messages screen is split into three modes — **DMs**, **Channels**, and **Rooms** — selectable with UP/DOWN on the mode-select screen. Each mode shows the corresponding list of conversations with unread counters.
 
@@ -16,7 +16,7 @@ The Messages screen is split into three modes — **DMs**, **Channels**, and **R
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_2_oled.png) | ![](./mes_scr_2_eink.png) |
+| ![](./compose_oled.png) | ![](./compose_eink.png) |
 
 Press **Enter** on a contact or channel to open its history, then press **Enter** again (or select an empty send row) to compose a message. Choose between:
 
@@ -44,7 +44,7 @@ Sensor placeholders appear automatically in the placeholder picker when the corr
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_3_oled.png) | ![](./mes_scr_3_eink.png) |
+| ![](./history_oled.png) | ![](./history_eink.png) |
 
 Each entry in the history list shows the sender name and a compact age indicator (`3m`, `2h`, `>1d`) in the top-right corner.
 
@@ -56,7 +56,7 @@ Each entry in the history list shows the sender name and a compact age indicator
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_4_oled.png) | ![](./mes_scr_4_eink.png) |
+| ![](./fullscreen_oled.png) | ![](./fullscreen_eink.png) |
 
 Navigate between messages with **LEFT** (newer) and **RIGHT** (older). Long messages scroll with **UP/DOWN**.
 
@@ -64,7 +64,7 @@ If the message is a reply addressed to someone (`@[nick]`), a **To: nick** bar i
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_5_oled.png) | ![](./mes_scr_5_eink.png) |
+| ![](./fullscreen_menu_oled.png) | ![](./fullscreen_menu_eink.png) |
 
 **Hold Enter** in fullscreen opens the options menu. It always offers **Reply** for an incoming message, and when the message contains a **location** it adds two more:
 
@@ -81,7 +81,7 @@ A location is any `lat,lon` pair in the text — exactly what the `{loc}` placeh
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_6_oled.png) | ![](./mes_scr_6_eink.png) |
+| ![](./ctx_contact_oled.png) | ![](./ctx_contact_eink.png) |
 
 | Item                         | Action                                                                         |
 | ---------------------------- | ------------------------------------------------------------------------------ |
@@ -98,7 +98,7 @@ When **Pin to dial** is selected, a slot picker opens (Slot 1–6 showing curren
 
 |           OLED            |           E-Ink           |
 | :-----------------------: | :-----------------------: |
-| ![](./mes_scr_7_oled.png) | ![](./mes_scr_7_eink.png) |
+| ![](./ctx_channel_oled.png) | ![](./ctx_channel_eink.png) |
 
 **Hold Enter** on a channel entry opens a context menu: