SSE EventSource connections for AIS, ACARS, VDL2, and radiosonde were
not closed when switching modes, causing fd exhaustion after repeated
switches. Also fixes socket leaks on exception paths in AIS/ADS-B
stream parsers, closes subprocess pipes in safe_terminate/cleanup, and
caches skyfield timescale at module level to avoid per-request fd churn.
Closes#169
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add VDL2 (VHF Digital Link Mode 2) decoding via dumpvdl2 as a new mode,
and promote ACARS from ADS-B-dashboard-only to a first-class standalone
mode in the main SPA. Both aviation datalink modes now have full nav
entries, sidebar partials with region-based frequency selectors, and
SSE streaming. VDL2 also integrated into the ADS-B dashboard as a
collapsible sidebar alongside ACARS.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
