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/hygiene.rs

@@ -0,0 +1,60 @@
+// 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.
+
+// Make sure that macro hygiene will ensure that when we reference "zerocopy",
+// that will work properly even if they've renamed the crate and have not
+// imported its traits.
+
+// See comment in `include.rs` for why we disable the prelude.
+#![no_implicit_prelude]
+#![allow(warnings)]
+
+include!("include.rs");
+
+extern crate zerocopy_renamed as _zerocopy;
+
+#[derive(_zerocopy::KnownLayout, _zerocopy::FromBytes, _zerocopy::Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct TypeParams<'a, T, I: imp::Iterator> {
+    a: T,
+    c: I::Item,
+    d: u8,
+    e: imp::PhantomData<&'a [::core::primitive::u8]>,
+    f: imp::PhantomData<&'static ::core::primitive::str>,
+    g: imp::PhantomData<imp::String>,
+}
+
+util_assert_impl_all!(
+    TypeParams<'static, (), imp::IntoIter<()>>:
+        _zerocopy::KnownLayout,
+        _zerocopy::FromZeros,
+        _zerocopy::FromBytes,
+        _zerocopy::Unaligned
+);
+
+// Regression test for #2177.
+//
+// This test ensures that `#[derive(KnownLayout)]` does not trigger the
+// `private_bounds` lint when used on a public struct in a macro.
+mod issue_2177 {
+    #![deny(private_bounds)]
+    // We need to access `_zerocopy` from the parent module.
+    use super::_zerocopy;
+
+    macro_rules! define {
+        ($name:ident, $repr:ty) => {
+            #[derive(_zerocopy::KnownLayout)]
+            #[zerocopy(crate = "zerocopy_renamed")]
+            #[repr(C)]
+            pub struct $name($repr);
+        };
+    }
+
+    define!(Foo, u8);
+}