gpsd sends multiple SKY messages per cycle — some contain only DOP
values with an empty satellites array. Previously this would overwrite
the satellite list, causing the sky view to flicker empty. Now DOP-only
SKY messages preserve the existing satellite list. Also adds a 5-second
polling fallback for satellite data since SSE can miss sky updates due
to queue contention.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>