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>

release-notes.md

@@ -0,0 +1,31 @@
+## MeshCore Solo Companion Firmware v1.21
+
+### What's new
+
+- **Live Location Sharing** — broadcast your position over the mesh as `[LOC]` messages, **movement-gated**, to a channel or a single contact. Others who share theirs show up as pins on the map with live **distance/bearing in Nearby Nodes**, and a **status-bar indicator** appears while your own share is active. `[LOC]` is parsed in DMs, channel messages **and room messages**; DM shares name the sender.
+- **Locator** (geofence) — arm a geofence around a **target** — a saved waypoint *or* a person (their live `[LOC]` or last-known position) — and get an alert when you **arrive/leave** or they get **near/far**, with an optional **homing beeper** that ticks faster the closer you get (and overrides a muted buzzer). Arm it from **Tools › Locator** or straight from **Nearby Nodes** / **Waypoints**; pick the target from a list (favourites first, then any contact), and clear it via a **"None"** entry. The active target is drawn as a **flag** on the map.
+- **One active target across Locator / Navigate / Map** — a single **"Set as target"** action everywhere, backed by a shared resolver that prefers a live `[LOC]` share over the last-advertised GPS, so the three features always agree on where you're headed.
+- **Follow live contacts** — **Navigate** to a contact who is live-sharing and the view **follows them as they move**, adding an **ETA** line. **Quick-share** your own position straight from the Map.
+- **Map & status-bar upgrades** — the home mini-map gains a **north marker** and a **scale tick**; the status line shows the tracked-node count and, with a fix, an **arrow + distance to the nearest tracked contact** (e.g. `Track:3 →120m`); a **GPS fix icon** sits in the top status bar (boxed once a fix is valid, plain while searching), shown only on GPS boards while **GPS** is enabled in Settings.
+- **Trail auto-pause** — recording **freezes on stops** (banking elapsed time and breaking the map line across the idle gap) and **resumes on movement** without ending the session; the home-screen blink keeps going while paused.
+- **Collapsible Tools** — tools are grouped into fold-in-place **Location / Comms / System** sections, the same model as Settings (Tools always opens folded to the section list), and the home carousel now uses **page-indicator icons** instead of dots.
+- **Waypoint coordinate editor** — add a waypoint by scroll-editing its latitude/longitude digit by digit.
+
+### Fixes
+
+- **Critical — low-heap hang and contact loss on RAM-tight builds.** With `MAX_CONTACTS=350` and `OFFLINE_QUEUE_SIZE=256` the device ran with very little free heap; an allocation in the input/menu path could then fail and **hang the UI** (notably when entering Diagnostics), and a crash or reset mid-save could **wipe all contacts**. Fixed by two independent changes:
+  - **Right-sized message-history rings** — the on-device scrollback rings were halved (96→48 channel, 64→32 DM), recovering **~14 KB of free heap** (measured 3 → 17 KB). History is RAM-only, so the only cost is shorter on-device scrollback.
+  - **Atomic persistence** — contacts, channels and prefs are now written to a temp file and **atomically renamed** into place; an interrupted save (crash, reset, full flash) leaves the previous good file intact instead of truncating it.
+- **USB host stall** — `Serial.write()` is bounded so a stalled USB host can no longer hang the device indefinitely.
+- **Nearby Nodes** — live `[LOC]` senders now respect the type filter and sort by their shared position; the distance-sorted list refreshes so live shares bubble to the top.
+- **Map** — live contacts are labelled before waypoints, so a person's name shows rather than a nearby waypoint's.
+- **GPS status icon** is hidden when GPS is turned off in Settings, instead of sitting there empty.
+- Null-guarded the Locator target picker and clamped the loc-share channel index on load.
+
+### Under the hood
+
+- **Streaming trail simplification** — GPS points are simplified as they're recorded via a fixed-corridor (Reumann–Witkam) pass: straight runs collapse to their two endpoints while curves stay bounded to within the **Min dist** tolerance of the real track, so the 512-point buffer covers a far longer route than a flat point budget would suggest. The buffer is kept at 512 points to bound the static RAM footprint on nRF52.
+- A UITask-decoupled active-target resolver (`resolvePersonPos` / `activeTargetPos`) replaces the duplicated target-resolution logic that lived separately in the Locator, Navigate and Map entry points.
+- `-Os` size optimisation on the e-ink and GAT562 30S solo envs to keep them within the flash budget.
+
+> **Upgrade note:** if a previous version lost your contacts after a hang, you'll need to re-add them once — the atomic-save protection applies from this release onward.