Rewrite MUX: WS2812C LEDs (NeoPixel) + 74HC165 buttons

PixelStomp MUX uses:
- WS2812C LEDs: one data line via DAT (GPIO 9), NeoPixel protocol
- 74HC165 shift register: LD/CLK/DI for reading 8 button states

Changes:
- Use Adafruit NeoPixel library for LED control
- Proper 74HC165 parallel-load shift-in for buttons
- 8 switches + 8 LEDs (was incorrectly 10)
- Diagnostic commands: dump, ledtest, red, green, blue, read

src/pixel_stomp_mux.cpp

@@ -3,116 +3,85 @@
 
 PixelStompMux::PixelStompMux(uint8_t dat, uint8_t ld, uint8_t clk, uint8_t di)
     : pin_dat(dat), pin_ld(ld), pin_clk(clk), pin_di(di),
-      last_button_state(0), current_led_state(0) {
+      strip(nullptr), last_button_state(0) {
 }
 
 void PixelStompMux::begin() {
-    pinMode(pin_dat, OUTPUT);
     pinMode(pin_ld, OUTPUT);
     pinMode(pin_clk, OUTPUT);
     pinMode(pin_di, INPUT_PULLUP);
 
-    digitalWrite(pin_dat, LOW);
     digitalWrite(pin_ld, LOW);
     digitalWrite(pin_clk, LOW);
 
+    strip = new Adafruit_NeoPixel(NUM_LEDS, pin_dat, NEO_GRB + NEO_KHZ800);
+    strip->begin();
+    strip->setBrightness(50);
+    strip->clear();
+    strip->show();
+
     Serial.printf("[MUX] Init DAT=%d LD=%d CLK=%d DI=%d\n",
                   pin_dat, pin_ld, pin_clk, pin_di);
-
-    Serial.println("[MUX] GPIO probe:");
-    Serial.printf("  DI (GPIO %d) reads: %d (should be 1 with pullup)\n",
-                  pin_di, digitalRead(pin_di));
-
-    for (int i = 0; i < 3; i++) {
-        digitalWrite(pin_clk, HIGH);
-        delayMicroseconds(10);
-        digitalWrite(pin_clk, LOW);
-        delayMicroseconds(10);
-    }
-    Serial.printf("  DI after 3 CLK pulses: %d\n", digitalRead(pin_di));
-
-    digitalWrite(pin_ld, HIGH);
-    delayMicroseconds(10);
-    digitalWrite(pin_ld, LOW);
-    delayMicroseconds(10);
-    Serial.printf("  DI after LD pulse: %d\n", digitalRead(pin_di));
+    Serial.printf("[MUX] 74HC165 for %d buttons, WS2812C for %d LEDs\n",
+                  NUM_BUTTONS, NUM_LEDS);
 }
 
-uint16_t PixelStompMux::read_buttons() {
-    pulse_pin(pin_ld, HIGH);
-    delayMicroseconds(10);
-    pulse_pin(pin_ld, LOW);
-    delayMicroseconds(10);
+uint8_t PixelStompMux::read_buttons() {
+    digitalWrite(pin_ld, HIGH);
+    delayMicroseconds(5);
+    digitalWrite(pin_ld, LOW);
+    delayMicroseconds(5);
 
-    uint16_t state = shift_in(NUM_INPUTS);
-    last_button_state = state;
-
-    return state;
+    last_button_state = shift_in_74hc165();
+    return last_button_state;
 }
 
 bool PixelStompMux::is_button_pressed(uint8_t index) {
-    if (index >= NUM_INPUTS) return false;
-
-    uint16_t state = read_buttons();
+    if (index >= NUM_BUTTONS) return false;
+    uint8_t state = read_buttons();
     return !(state & (1 << index));
 }
 
-void PixelStompMux::write_leds(uint16_t led_state) {
-    current_led_state = led_state;
-    shift_out(led_state, NUM_OUTPUTS);
-
-    pulse_pin(pin_ld, HIGH);
-    delayMicroseconds(10);
-    pulse_pin(pin_ld, LOW);
+void PixelStompMux::set_led_color(uint8_t index, uint8_t r, uint8_t g, uint8_t b) {
+    if (index >= NUM_LEDS || !strip) return;
+    strip->setPixelColor(index, strip->Color(r, g, b));
 }
 
-void PixelStompMux::set_led(uint8_t index, bool on) {
-    if (index >= NUM_OUTPUTS) return;
-
-    if (on) {
-        current_led_state |= (1 << index);
-    } else {
-        current_led_state &= ~(1 << index);
-    }
-
-    write_leds(current_led_state);
+void PixelStompMux::set_led_brightness(uint8_t brightness) {
+    if (strip) strip->setBrightness(brightness);
 }
 
 void PixelStompMux::clear_all() {
-    write_leds(0x0000);
-    Serial.println("[MUX] All LEDs off");
+    if (strip) {
+        strip->clear();
+        strip->show();
+    }
+    Serial.println("[MUX] LEDs cleared");
+}
+
+void PixelStompMux::show() {
+    if (strip) strip->show();
 }
 
 void PixelStompMux::dump() {
-    uint16_t buttons = read_buttons();
-    Serial.printf("[MUX] Buttons: 0x%03X LEDs: 0x%03X\n", buttons, current_led_state);
+    uint8_t buttons = read_buttons();
+    Serial.printf("[MUX] Buttons: 0x%02X (binary: ", buttons);
+    for (int i = 7; i >= 0; i--) {
+        Serial.print((buttons >> i) & 1);
+    }
+    Serial.println(")");
 
-    for (int i = 0; i < NUM_INPUTS; i++) {
+    for (int i = 0; i < NUM_BUTTONS; i++) {
         bool pressed = !(buttons & (1 << i));
-        bool led_on = current_led_state & (1 << i);
-        Serial.printf("  [%d] Button:%s LED:%s\n", i,
-                      pressed ? "PRESS" : "off",
-                      led_on ? "ON" : "off");
+        Serial.printf("  [%d] %s\n", i, pressed ? "PRESS" : "off");
     }
 }
 
-void PixelStompMux::shift_out(uint16_t data, uint8_t bits) {
-    for (int i = bits - 1; i >= 0; i--) {
-        digitalWrite(pin_dat, (data >> i) & 1);
-        delayMicroseconds(1);
-        digitalWrite(pin_clk, HIGH);
-        delayMicroseconds(1);
-        digitalWrite(pin_clk, LOW);
-        delayMicroseconds(1);
-    }
-}
+uint8_t PixelStompMux::shift_in_74hc165() {
+    uint8_t data = 0;
 
-uint16_t PixelStompMux::shift_in(uint8_t bits) {
-    uint16_t data = 0;
-
-    for (int i = bits - 1; i >= 0; i--) {
-        bool bit = digitalRead(pin_di);
-        if (bit) {
+    for (int i = NUM_BUTTONS - 1; i >= 0; i--) {
+        if (digitalRead(pin_di)) {
             data |= (1 << i);
         }
         digitalWrite(pin_clk, HIGH);
@@ -123,8 +92,3 @@ uint16_t PixelStompMux::shift_in(uint8_t bits) {
 
     return data;
 }
-
-void PixelStompMux::pulse_pin(uint8_t pin, uint8_t level, uint16_t duration_us) {
-    digitalWrite(pin, level);
-    delayMicroseconds(duration_us);
-}