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/zerocopy-derive/tests/struct_known_layout.rs

@@ -0,0 +1,131 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// See comment in `include.rs` for why we disable the prelude.
+#![no_implicit_prelude]
+#![allow(warnings)]
+
+extern crate rustversion;
+
+include!("include.rs");
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+struct Zst;
+
+util_assert_impl_all!(Zst: imp::KnownLayout);
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+struct One {
+    a: bool,
+}
+
+util_assert_impl_all!(One: imp::KnownLayout);
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+struct Two {
+    a: bool,
+    b: Zst,
+}
+
+util_assert_impl_all!(Two: imp::KnownLayout);
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+struct TypeParams<'a, T, I: imp::Iterator> {
+    a: I::Item,
+    b: u8,
+    c: imp::PhantomData<&'a [::core::primitive::u8]>,
+    d: imp::PhantomData<&'static ::core::primitive::str>,
+    e: imp::PhantomData<imp::String>,
+    f: T,
+}
+
+util_assert_impl_all!(TypeParams<'static, (), imp::IntoIter<()>>: imp::KnownLayout);
+util_assert_impl_all!(TypeParams<'static, util::AU16, imp::IntoIter<()>>: imp::KnownLayout);
+
+// Deriving `KnownLayout` should work if the struct has bounded parameters.
+//
+// N.B. We limit this test to rustc >= 1.62, since earlier versions of rustc ICE
+// when `KnownLayout` is derived on a `repr(C)` struct whose trailing field
+// contains non-static lifetimes.
+#[rustversion::since(1.62)]
+const _: () = {
+    #[derive(imp::KnownLayout)]
+    #[zerocopy(crate = "zerocopy_renamed")]
+    #[repr(C)]
+    struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + imp::KnownLayout, const N: usize>(
+        [T; N],
+        imp::PhantomData<&'a &'b ()>,
+    )
+    where
+        'a: 'b,
+        'b: 'a,
+        T: 'a + 'b + imp::KnownLayout;
+
+    util_assert_impl_all!(WithParams<'static, 'static, u8, 42>: imp::KnownLayout);
+};
+
+const _: () = {
+    // Similar to the previous test, except that the trailing field contains
+    // only static lifetimes. This is exercisable on all supported toolchains.
+
+    #[derive(imp::KnownLayout)]
+    #[zerocopy(crate = "zerocopy_renamed")]
+    #[repr(C)]
+    struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + imp::KnownLayout, const N: usize>(
+        &'a &'b [T; N],
+        imp::PhantomData<&'static ()>,
+    )
+    where
+        'a: 'b,
+        'b: 'a,
+        T: 'a + 'b + imp::KnownLayout;
+
+    util_assert_impl_all!(WithParams<'static, 'static, u8, 42>: imp::KnownLayout);
+};
+
+// Deriving `KnownLayout` should work if the struct references `Self`. See
+// #2116.
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct WithSelfReference {
+    leading: [u8; Self::N],
+    trailing: [[u8; Self::N]],
+}
+
+impl WithSelfReference {
+    const N: usize = 42;
+}
+
+util_assert_impl_all!(WithSelfReference: imp::KnownLayout);
+
+// Deriving `KnownLayout` should work with generic `repr(packed)` types. See
+// #2302.
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C, packed)]
+struct Packet<P> {
+    payload: P,
+}
+
+util_assert_impl_all!(Packet<imp::u8>: imp::KnownLayout);
+
+#[derive(imp::KnownLayout)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct RawIdentifier {
+    r#type: u8,
+}
+
+util_assert_impl_all!(RawIdentifier: imp::KnownLayout);