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/channels.h

@@ -0,0 +1,24 @@
+#ifndef CHANNELS_H
+#define CHANNELS_H
+
+#include <stdint.h>
+#include <stddef.h>
+#include "board.h"
+
+void channels_init(void);
+
+/** Returns pointer to 512 channel values for universe index 0 or 1 (no start code). */
+uint8_t *channels_get(unsigned universe);
+
+/** Build a 513-byte DMX frame (start code 0 + 512 channels) into out. */
+void channels_build_frame(unsigned universe, uint8_t out[BOARD_DMX_FRAME_LEN]);
+
+void channels_set(unsigned universe, unsigned channel, uint8_t value);
+void channels_set_range(unsigned universe, const uint8_t *values, size_t len);
+void channels_clear(unsigned universe);
+
+void channels_note_artnet(unsigned universe);
+uint32_t channels_artnet_packets(void);
+uint32_t channels_ms_since_artnet(unsigned universe);
+
+#endif