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/union_unaligned.rs

@@ -0,0 +1,80 @@
+// 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 union 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)]
+union Foo {
+    a: imp::u8,
+}
+
+util_assert_impl_all!(Foo: imp::Unaligned);
+
+// Transparent unions are unstable; see issue #60405
+// <https://github.com/rust-lang/rust/issues/60405> for more information.
+
+// #[derive(Unaligned)]
+// #[repr(transparent)]
+// union Bar {
+//     a: u8,
+// }
+
+// is_unaligned!(Bar);
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(packed)]
+union 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))]
+union FooAlign {
+    a: imp::u8,
+}
+
+util_assert_impl_all!(FooAlign: imp::Unaligned);
+
+#[derive(imp::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union TypeParams<'a, T: imp::Copy, I: imp::Iterator>
+where
+    I::Item: imp::Copy,
+{
+    a: T,
+    c: I::Item,
+    d: u8,
+    e: imp::PhantomData<&'a [imp::u8]>,
+    f: imp::PhantomData<&'static imp::str>,
+    g: imp::PhantomData<imp::String>,
+}
+
+util_assert_impl_all!(TypeParams<'static, (), imp::IntoIter<()>>: imp::Unaligned);