feat: port MT76 radio init and CLI tool

Complete the radio bring-up sequence: init_registers now writes the
upstream register values (PBF out of reset, beacon TX off), crystal
calibration, MAC/BSSID programming, channel evaluation, and beacon
programming through an MCU burst into PBF shared memory. The beacon
txwi is the full 20-byte struct and the RF patch is applied on the
cold firmware path.

Download firmware per product (xone_dongle_02e6.bin / 02fe.bin) and
add the xone_cli debug tool (info, firmware, radio-init/deinit, burst,
reg-read/write, led, recover). Recover uses USBDeviceReEnumerate for a
host-side port reset.

Co-Authored-By: grok4.6: internet search (firmware split, beacon SRAM, upstream issues)
Co-Authored-By: qwen3.8-27b@q2_k_xl: initial radio init and CLI implementation
Co-Authored-By: deepseek/deepseek-v4-pro-0813: final radio init fixes and verification

include/common/log.hpp

@@ -43,6 +43,7 @@ inline auto log_msg(log_level level, char const* fmt, ...) -> void
     std::vfprintf(stderr, fmt, ap);
     va_end(ap);
     std::fprintf(stderr, "\n");
+    std::fflush(stderr);   // The app is often killed; do not lose the tail.
 }
 
 } // namespace xone