refactor: unify SimpleLed via embedded-hal, remove Option<L> from BoardParts

- Added embedded-hal 1.0 as direct dep (already transitive via embedded-hal-async)
- SimpleLed<P: OutputPin> now generic over any HAL — single definition in driver/
- Removed duplicate SimpleLed from board/esp32s3.rs and board/wio_tracker_l1.rs
- Changed BoardParts.led from Option<L> to L — boards with no LED use ()
- Display task calls led.set_rgb() unconditionally (no-op for () boards)
- RAK board: led: () instead of led: None

src/driver/mod.rs

@@ -1,2 +1,5 @@
 #[cfg(feature = "wio_tracker_l1")]
 pub mod sh1106;
+
+#[cfg(any(feature = "heltec_v3", feature = "heltec_v3_uart", feature = "heltec_v4", feature = "wio_tracker_l1"))]
+pub mod simple_led;

src/driver/simple_led.rs

@@ -0,0 +1,20 @@
+//! Simple single-color LED driver (GPIO on/off).
+//!
+//! Generic over any `OutputPin`. Any non-zero RGB value turns the LED on;
+//! all zeros turns it off.
+
+use embedded_hal::digital::OutputPin;
+
+use crate::board::RgbLed;
+
+pub struct SimpleLed<P>(pub P);
+
+impl<P: OutputPin> RgbLed for SimpleLed<P> {
+    async fn set_rgb(&mut self, r: u8, g: u8, b: u8) {
+        if r > 0 || g > 0 || b > 0 {
+            let _ = self.0.set_high();
+        } else {
+            let _ = self.0.set_low();
+        }
+    }
+}