feat(01-01): LED driver — dual strip initialization and output

- led_driver.h declares StripWand (NeoGrbwFeature/RMT) + StripSchrank (NeoWs2801Spi2MhzMethod)
- led_driver.cpp implements initStrips, showBothStrips, setAllWand/Schrank, applyBrightness helpers
- showBothStrips calls stripWand.Show() first (non-blocking DMA) then stripSchrank.Show() (blocking SPI)
- Brightness clamped to [0.0f, BRIGHTNESS_MAX] before scaling

firmware/src/led_driver.h

@@ -0,0 +1,18 @@
+#pragma once
+#include <NeoPixelBus.h>
+#include "config.h"
+
+// SK6812: RGBW (4 bytes/LED) — MUST use NeoGrbwFeature, never NeoRgbFeature
+using StripWand    = NeoPixelBus<NeoGrbwFeature, NeoEsp32Rmt0Ws2812xMethod>;
+// WS2801: RGB (3 bytes/LED), 2MHz SPI for cable-safe 5m run
+using StripSchrank = NeoPixelBus<NeoRgbFeature, NeoWs2801Spi2MhzMethod>;
+
+extern StripWand    stripWand;
+extern StripSchrank stripSchrank;
+
+void initStrips();
+void showBothStrips();
+void setAllWand(RgbwColor color);
+void setAllSchrank(RgbColor color);
+RgbwColor applyBrightnessW(RgbwColor c, float factor);
+RgbColor  applyBrightnessR(RgbColor c, float factor);