feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/bytemuck/src/zeroable_in_option.rs

@@ -0,0 +1,77 @@
+use super::*;
+
+// Note(Lokathor): This is the neat part!!
+unsafe impl<T: ZeroableInOption> Zeroable for Option<T> {}
+
+/// Trait for types which are [Zeroable](Zeroable) when wrapped in
+/// [Option](core::option::Option).
+///
+/// ## Safety
+///
+/// * `Option<YourType>` must uphold the same invariants as
+///   [Zeroable](Zeroable).
+pub unsafe trait ZeroableInOption: Sized {}
+
+unsafe impl ZeroableInOption for NonZeroI8 {}
+unsafe impl ZeroableInOption for NonZeroI16 {}
+unsafe impl ZeroableInOption for NonZeroI32 {}
+unsafe impl ZeroableInOption for NonZeroI64 {}
+unsafe impl ZeroableInOption for NonZeroI128 {}
+unsafe impl ZeroableInOption for NonZeroIsize {}
+unsafe impl ZeroableInOption for NonZeroU8 {}
+unsafe impl ZeroableInOption for NonZeroU16 {}
+unsafe impl ZeroableInOption for NonZeroU32 {}
+unsafe impl ZeroableInOption for NonZeroU64 {}
+unsafe impl ZeroableInOption for NonZeroU128 {}
+unsafe impl ZeroableInOption for NonZeroUsize {}
+
+// Note: this does not create NULL vtable because we get `None` anyway.
+unsafe impl<T: ?Sized> ZeroableInOption for NonNull<T> {}
+unsafe impl<T: ?Sized> ZeroableInOption for &'_ T {}
+unsafe impl<T: ?Sized> ZeroableInOption for &'_ mut T {}
+
+#[cfg(feature = "extern_crate_alloc")]
+#[cfg_attr(feature = "nightly_docs", doc(cfg(feature = "extern_crate_alloc")))]
+unsafe impl<T: ?Sized> ZeroableInOption for alloc::boxed::Box<T> {}
+
+#[cfg(feature = "zeroable_unwind_fn")]
+macro_rules! impl_for_unwind_fn {
+    ($($ArgTy:ident),* $(,)?) => {
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for extern "C-unwind" fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for unsafe extern "C-unwind" fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for extern "system-unwind" fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for unsafe extern "system-unwind" fn($($ArgTy,)*) -> R {}
+    };
+}
+
+macro_rules! impl_for_fn {
+    ($($ArgTy:ident),* $(,)?) => {
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for unsafe fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for extern "C" fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for unsafe extern "C" fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for extern "system" fn($($ArgTy,)*) -> R {}
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for unsafe extern "system" fn($($ArgTy,)*) -> R {}
+        #[cfg(all(target_os="windows", target_arch = "x86"))]
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for extern "stdcall" fn($($ArgTy,)*) -> R {}
+        #[cfg(all(target_os="windows", target_arch = "x86"))]
+        unsafe impl<$($ArgTy,)* R> ZeroableInOption for unsafe extern "stdcall" fn($($ArgTy,)*) -> R {}
+        #[cfg(feature = "zeroable_unwind_fn")]
+        impl_for_unwind_fn!($($ArgTy),*);
+    };
+}
+
+impl_for_fn!();
+impl_for_fn!(A);
+impl_for_fn!(A, B);
+impl_for_fn!(A, B, C);
+impl_for_fn!(A, B, C, D);
+impl_for_fn!(A, B, C, D, E);
+impl_for_fn!(A, B, C, D, E, F);
+impl_for_fn!(A, B, C, D, E, F, G);
+impl_for_fn!(A, B, C, D, E, F, G, H);
+impl_for_fn!(A, B, C, D, E, F, G, H, I);
+impl_for_fn!(A, B, C, D, E, F, G, H, I, J);
+impl_for_fn!(A, B, C, D, E, F, G, H, I, J, K);
+impl_for_fn!(A, B, C, D, E, F, G, H, I, J, K, L);
+impl_for_fn!(A, B, C, D, E, F, G, H, I, J, K, L, M);