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/dmx_out.h

@@ -0,0 +1,21 @@
+#ifndef DMX_OUT_H
+#define DMX_OUT_H
+
+#include <stdbool.h>
+#include <stdint.h>
+#include "hardware/pio.h"
+
+typedef struct {
+    PIO pio;
+    uint sm;
+    uint dma;
+    uint pin;
+    uint prgm_offset;
+    bool inited;
+} dmx_out_t;
+
+bool dmx_out_init(dmx_out_t *out, uint pin, PIO pio);
+void dmx_out_write(dmx_out_t *out, const uint8_t *frame, uint length);
+bool dmx_out_busy(const dmx_out_t *out);
+
+#endif