Replaces the single secondary_sdr_mode with secondary_sdr_priority, e.g. ["adsb", "ais"]. OP25 always keeps its own dongle; the secondary-sdr container starts decoders top-down until it runs out of free SDRs, so a 3-SDR node runs ADS-B and AIS at once and a 2-SDR node runs the top pick. - secondary-sdr: one decoder per mode, POST /secondary/apply(priority) (no-op when the right prefix is already running), orphaned decoders from a uvicorn reload are reaped on start, /status reports sdr_count via lsusb (op25's :stable image has none). - edge-node: one apply path (set_secondary_priority) for the local dashboard, a new C2 'set_secondary_priority' MQTT command, and config pushes; it never restarts op25. Legacy mode migrates on load. Checkin reports priority, what's running, and sdr_count. Uplink forwards aircraft and vessels whenever either is present. - Local dashboard: 'Secondary SDRs' card to enable/reorder/save. Verified: edge-node pytest 190 passed, flake8 clean. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>