Add ArtNetDMX Pico W firmware with dual DMX and docs.

Art-Net to two RS-485 outputs over Wi-Fi (AP or STA with SoftAP fallback), web UI, mDNS, and QLC+/ArtPoll notes for unicast on STA.

Co-authored-by: Cursor <cursoragent@cursor.com>

include/artnet.h

@@ -0,0 +1,14 @@
+#ifndef ARTNET_H
+#define ARTNET_H
+
+#include <stdbool.h>
+
+bool artnet_start(void);
+/** Re-bind listeners to current AP/STA IPs (call after SoftAP re-assert or STA join). */
+void artnet_refresh(void);
+/** Broadcast ArtPollReply (call after interface comes up). */
+void artnet_announce(void);
+/** Periodic discovery announces (call from main loop). */
+void artnet_poll(void);
+
+#endif