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_unaligned.rs

@@ -0,0 +1,103 @@
+// Copyright 2019 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)]
+
+include!("include.rs");
+
+// A struct is `Unaligned` if:
+// - `repr(align)` is no more than 1 and either
+//   - `repr(C)` or `repr(transparent)` and
+//     - all fields Unaligned
+//   - `repr(packed)`
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct Foo {
+    a: u8,
+}
+
+util_assert_impl_all!(Foo: imp::Unaligned);
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(transparent)]
+struct Bar {
+    a: u8,
+}
+
+util_assert_impl_all!(Bar: imp::Unaligned);
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(packed)]
+struct Baz {
+    // NOTE: The `u16` type is not guaranteed to have alignment 2, although it
+    // does on many platforms. However, to fix this would require a custom type
+    // with a `#[repr(align(2))]` attribute, and `#[repr(packed)]` types are not
+    // allowed to transitively contain `#[repr(align(...))]` types. Thus, we
+    // have no choice but to use `u16` here. Luckily, these tests run in CI on
+    // platforms on which `u16` has alignment 2, so this isn't that big of a
+    // deal.
+    a: u16,
+}
+
+util_assert_impl_all!(Baz: imp::Unaligned);
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C, align(1))]
+struct FooAlign {
+    a: u8,
+}
+
+util_assert_impl_all!(FooAlign: imp::Unaligned);
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(transparent)]
+struct Unsized {
+    a: [u8],
+}
+
+util_assert_impl_all!(Unsized: imp::Unaligned);
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct TypeParams<'a, T: ?imp::Sized, 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::Unaligned);
+util_assert_impl_all!(TypeParams<'static, ::core::primitive::u8, imp::IntoIter<()>>: imp::Unaligned);
+util_assert_impl_all!(TypeParams<'static, [::core::primitive::u8], imp::IntoIter<()>>: imp::Unaligned);
+
+// Deriving `Unaligned` should work if the struct has bounded parameters.
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(transparent)]
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + imp::Unaligned, const N: usize>(
+    [T; N],
+    imp::PhantomData<&'a &'b ()>,
+)
+where
+    'a: 'b,
+    'b: 'a,
+    T: 'a + 'b + imp::Unaligned;
+
+util_assert_impl_all!(WithParams<'static, 'static, u8, 42>: imp::Unaligned);