The fft_reader thread was calling ws.send() concurrently with
ws.receive() in the main loop. simple-websocket is not thread-safe
for simultaneous read/write, corrupting frame headers. Now the reader
thread enqueues frames and only the main loop touches the WebSocket.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Replace the batch rtl_power SSE pipeline with continuous I/Q streaming
via WebSocket for smooth ~25fps waterfall display. The server captures
raw I/Q samples (rtl_sdr/rx_sdr), computes Hann-windowed FFT, and
sends compact binary frames (1035 bytes vs ~15KB JSON, 93% reduction).
Client falls back to existing SSE path if WebSocket is unavailable.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
