Add PixelStomp MUX driver (DAT=9, LD=10, CLK=11, DI=12)

- New PixelStompMux class with shift register read/write
- Read 10 buttons via DI (active LOW)
- Drive 10 LEDs via DAT (shift out + latch)
- LED startup animation uses MUX
- Switch polling reads from MUX shift register
- MUX instance shared between switch and LED drivers

src/pixel_stomp_mux.cpp

@@ -0,0 +1,110 @@
+#include "pixel_stomp_mux.h"
+#include <Arduino.h>
+
+static const char* TAG = "MUX";
+
+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) {
+}
+
+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);
+
+    Serial.printf("[MUX] Init DAT=%d LD=%d CLK=%d DI=%d\n",
+                  pin_dat, pin_ld, pin_clk, pin_di);
+}
+
+uint16_t PixelStompMux::read_buttons() {
+    pulse_pin(pin_ld, HIGH);
+    delayMicroseconds(5);
+    pulse_pin(pin_ld, LOW);
+    delayMicroseconds(5);
+
+    uint16_t state = shift_in(NUM_INPUTS);
+    last_button_state = state;
+
+    return state;
+}
+
+bool PixelStompMux::is_button_pressed(uint8_t index) {
+    if (index >= NUM_INPUTS) return false;
+
+    uint16_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(5);
+    pulse_pin(pin_ld, LOW);
+}
+
+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::clear_all() {
+    write_leds(0x0000);
+    Serial.println("[MUX] All LEDs off");
+}
+
+void PixelStompMux::dump() {
+    uint16_t buttons = read_buttons();
+    Serial.printf("[MUX] Buttons: 0x%03X LEDs: 0x%03X\n", buttons, current_led_state);
+
+    for (int i = 0; i < NUM_INPUTS; i++) {
+        bool pressed = !(buttons & (1 << i));
+        bool led_on = current_led_state & (1 << i);
+        if (pressed || led_on) {
+            Serial.printf("  [%d] Button:%s LED:%s\n", i,
+                          pressed ? "PRESS" : "off",
+                          led_on ? "ON" : "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);
+        pulse_pin(pin_clk, HIGH);
+        pulse_pin(pin_clk, LOW);
+    }
+}
+
+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) {
+            data |= (1 << i);
+        }
+        pulse_pin(pin_clk, HIGH);
+        pulse_pin(pin_clk, LOW);
+    }
+
+    return data;
+}
+
+void PixelStompMux::pulse_pin(uint8_t pin, uint8_t level, uint16_t duration_us) {
+    digitalWrite(pin, level);
+    delayMicroseconds(duration_us);
+}