The registry used plain int keys (device index), so HackRF at index 0
and RTL-SDR at index 0 would collide. Changed to composite string keys
("sdr_type:index") so each SDR type+index pair is tracked independently.
Updated all route callers, frontend device selectors, and session restore.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Implement HF radiofax decoding with custom Python DSP pipeline
(rtl_fm USB → Goertzel/Hilbert demodulation), 33-station database
with broadcast schedules, audio waveform scope, live image preview,
and decoded image gallery. Amber/gold UI theme for HF distinction.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>