feat: pair controllers and show them in the app

Port the MT76 client functions (send_wlan, associate_client,
pair_client, set_client_key, remove_client) and wire the RX dispatch
into the session: EP IN frames are parsed, ASSOC_REQ associates a
controller (WCID plus chip programming), PAIR_REQ replies with
PAIR_RESP, and DISASSOC or client-lost removes it. The C API exposes
connected controllers and the app lists them by MAC. Bumps
xone_cli/xone_app to C++23: they were falling back to the default
standard once mt76.hpp started using std::span. Adds a unit test pinning
the WCID regions, the 32-byte rxwi, and the new frame control values.

Co-Authored-By: qwen3.8-27b@q2_k_xl: client functions, RX dispatch, GUI list

include/mt76/mt76.hpp

@@ -12,6 +12,7 @@
 #include <array>
 #include <cstddef>
 #include <cstdint>
+#include <span>
 
 #include "mt76/mt76_defs.hpp"
 
@@ -55,7 +56,7 @@ public:
     auto select_function(std::uint32_t func, std::uint32_t val) -> int;
     auto set_power_mode(power_mode mode) -> int;
     auto load_cr(cr_mode mode) -> int;
-    auto write_burst(std::uint32_t idx, void *data, std::size_t len) -> int;
+    auto write_burst(std::uint32_t idx, void const *data, std::size_t len) -> int;
     auto send_ms_command(ms_command cmd, void *data, std::size_t len) -> int;
     auto calibrate(calibration calib, std::uint32_t val) -> int;
 
@@ -69,6 +70,37 @@ public:
     // Enter or leave pairing mode (port of xone_mt76_set_pairing).
     auto set_pairing(bool enable) -> int;
 
+    // Controller association and data path (ports of the xone_mt76_* client
+    // functions). `addr` is a 6-byte controller MAC.
+    //
+    // send_wlan prepends a TXWI and frames the payload as an MCU message,
+    // then bulk-writes it to EP OUT.
+    auto send_wlan(std::span<std::uint8_t const> frame) -> int;
+
+    // Associate a controller: program its WCID MAC, ADD_CLIENT ms_command,
+    // and transmit an ASSOC_RESP mgmt frame.
+    auto associate_client(std::uint8_t wcid, std::span<std::uint8_t const> addr)
+        -> int;
+
+    // Reply to a pairing request with a PAIR_RESP mgmt frame.
+    auto pair_client(std::span<std::uint8_t const> addr) -> int;
+
+    // Send a reserved (0x70) management command to a client, waiting for an
+    // acknowledgment (port of xone_mt76_send_client_command).
+    auto send_client_command(std::uint8_t wcid,
+                             std::span<std::uint8_t const> addr,
+                             client_cmd cmd,
+                             std::span<std::uint8_t const> data) -> int;
+
+    // Install the per-client AES-CCMP key (16 bytes) in the chip WCID
+    // registers (port of xone_mt76_set_client_key).
+    auto set_client_key(std::uint8_t wcid, std::span<std::uint8_t const> key)
+        -> int;
+
+    // Remove a client: REMOVE_CLIENT ms_command and zero its WCID regions
+    // (port of xone_mt76_remove_client).
+    auto remove_client(std::uint8_t wcid) -> int;
+
 private:
     // Send an MCU command (port of xone_mt76_send_command). `cmd` is the
     // MT_MCU_MSG_CMD_TYPE field. Returns bytes written, or a negative errno.