Add multi-panel Pico UDP firmware and Python LED control.

Pico panels get static IPs on 10.1.1.10–14 with per-panel LED counts, Makefile deploy targets, and Python examples for animations, sync tests, and direct Pi SPI control.

Co-authored-by: Cursor <cursoragent@cursor.com>

leds/backends/ws281x.py

@@ -0,0 +1,73 @@
+"""WS2812 via PWM/DMA — Pi 4 and Zero only (not Pi 5)."""
+
+from __future__ import annotations
+
+try:
+    from rpi_ws281x import PixelStrip, ws
+except ImportError as exc:  # pragma: no cover - import guard
+    PixelStrip = None
+    ws = None
+    _WS281X_IMPORT_ERROR = exc
+else:
+    _WS281X_IMPORT_ERROR = None
+
+
+class Ws281xBackend:
+    def __init__(
+        self,
+        led_count: int,
+        *,
+        pin: int = 18,
+        freq_hz: int = 800_000,
+        dma: int = 10,
+        invert: bool = False,
+        channel: int = 0,
+    ) -> None:
+        if PixelStrip is None:
+            raise ImportError(
+                "rpi-ws281x is required for the ws281x backend; install portal requirements"
+            ) from _WS281X_IMPORT_ERROR
+
+        self._led_count = led_count
+        self._strip = PixelStrip(
+            led_count,
+            pin,
+            freq_hz,
+            dma,
+            invert,
+            255,
+            channel,
+            strip_type=ws.WS2811_STRIP_GRB,
+        )
+        self._strip.begin()
+
+    @property
+    def led_count(self) -> int:
+        return self._led_count
+
+    def write_grb(self, grb_bytes: bytes) -> None:
+        if len(grb_bytes) != self._led_count * 3:
+            raise ValueError(
+                f"expected {self._led_count * 3} bytes, got {len(grb_bytes)}"
+            )
+
+        strip = self._strip
+        for i in range(self._led_count):
+            base = i * 3
+            g, r, b = grb_bytes[base], grb_bytes[base + 1], grb_bytes[base + 2]
+            strip.setPixelColor(i, (r << 16) | (g << 8) | b)
+        strip.show()
+
+    def clear(self) -> None:
+        for i in range(self._led_count):
+            self._strip.setPixelColor(i, 0)
+        self._strip.show()
+
+    def close(self) -> None:
+        self.clear()
+
+    def __enter__(self) -> Ws281xBackend:
+        return self
+
+    def __exit__(self, *_exc) -> None:
+        self.close()