- mcs_telemetry: fix snprintf truncation in to_json (advance offset by actual
bytes written, reserve tail for closing brackets)
- sd_card: use open/write/close instead of fwrite to bypass stdio buffering
- wifi_controller: append telemetry as NDJSON (one object per line)
- status_led: blink blue only when frames captured in monitor mode
Co-authored-by: Cursor <cursoragent@cursor.com>