feat(companion): follow live contacts — nav, geo-alert, ETA, quick-share

Builds on live location sharing:
- Nearby "Navigate" now follows a moving live target: the navigate view
  re-reads the shared position every second and re-locates the entry by
  name for non-contact senders, so it no longer freezes or drops out
  (previously only refreshed for stored contacts entered via detail).
- NavView gains a closing-speed / ETA line (EtaTracker), shown in the
  Nearby navigate view while approaching.
- Geo Alert target can be a live contact, not just a waypoint: the engine
  re-reads the contact's latest [LOC] position each evaluation (keyed by
  pubkey prefix) so the geofence follows a moving person; alert wording
  switches to Near/Away. The picker cycles waypoints + verified live
  contacts (shown with an '@' prefix). Schema bumped 0xC0DE0014 -> 0x15.
- Nearby marks a position-broadcasting node with the map's ♦ diamond
  (was a cryptic '*'/'~' prefix) and spells out "Sharing pos:" in detail.
- Home Map page Hold-Enter is a one-shot position share: pushes to the
  Live Share target while auto-sharing is on, else opens the picker.

Verified: WioTrackerL1_companion_solo_dual builds clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/LiveTrack.h

@@ -78,6 +78,19 @@ public:
     return n;
   }
 
+  // Latest active position for a verified (DM/pubkey) share, or null if that
+  // node hasn't shared recently. Used by the geo-alert engine to follow a
+  // moving contact.
+  const Entry* activeByKey(const uint8_t* key, uint32_t now) const {
+    if (!key) return nullptr;
+    for (int i = 0; i < CAPACITY; i++) {
+      if (!isActive(i, now)) continue;
+      const Entry& e = _e[i];
+      if (e.verified && memcmp(e.key, key, KEY_LEN) == 0) return &e;
+    }
+    return nullptr;
+  }
+
 private:
   Entry _e[CAPACITY] = {};