20.07 v0.2.1-dev

Small, targeted follow-up to v0.2.0-dev.

Live-confirmed a common trigger for "peer shows a hop count but never gets a radar dot": many
phones deliberately widen their reported GPS accuracy while stationary (to save battery), then
tighten it back up the instant motion is detected — so a dot could disappear while genuinely
standing still, even right next to the other phone, and reappear on the next step.

Raised the radar's combined-accuracy rejection threshold from 150m to 250m — comfortably above
the radar's own 200m display ceiling instead of sitting just under it — so this triggers less
often, while still rejecting genuinely rough (network-location-grade) fixes. The underlying
silent-failure UX gap (no on-screen explanation when this does trigger) is unchanged and still
tracked in README's Known Limitations.

Still pre-1.0. This is a debug build (unsigned release build does not exist yet).