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/enum_from_zeros.rs

@@ -0,0 +1,108 @@
+// 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");
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+enum Foo {
+    A,
+}
+
+util_assert_impl_all!(Foo: imp::FromZeros);
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+enum Bar {
+    A = 0,
+}
+
+util_assert_impl_all!(Bar: imp::FromZeros);
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+enum TwoVariantsHasExplicitZero {
+    A = 1,
+    B = 0,
+}
+
+util_assert_impl_all!(TwoVariantsHasExplicitZero: imp::FromZeros);
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(i8)]
+enum ImplicitNonFirstVariantIsZero {
+    A = -1,
+    B,
+}
+
+util_assert_impl_all!(ImplicitNonFirstVariantIsZero: imp::FromZeros);
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u64)]
+enum LargeDiscriminant {
+    A = 0xFFFF_FFFF_FFFF_FFFF,
+    B = 0x0000_0000_0000_0000,
+}
+
+util_assert_impl_all!(LargeDiscriminant: imp::FromZeros);
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+enum FirstVariantIsZeroable {
+    A(u32),
+    B { foo: u32 },
+}
+
+util_assert_impl_all!(FirstVariantIsZeroable: imp::FromZeros);
+
+#[derive(imp::FromZeros)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u8)]
+enum FirstVariantIsZeroableSecondIsNot {
+    A(bool),
+    B(::core::num::NonZeroU8),
+}
+
+util_assert_impl_all!(FirstVariantIsZeroableSecondIsNot: imp::FromZeros);
+
+// MSRV does not support data-carrying enum variants with explicit discriminants
+#[cfg(not(__ZEROCOPY_TOOLCHAIN = "msrv"))]
+mod msrv_only {
+    use super::*;
+
+    #[derive(imp::FromZeros)]
+    #[zerocopy(crate = "zerocopy_renamed")]
+    #[repr(u8)]
+    enum ImplicitFirstVariantIsZeroable {
+        A(bool),
+        B(::core::num::NonZeroU8) = 1,
+    }
+
+    util_assert_impl_all!(ImplicitFirstVariantIsZeroable: imp::FromZeros);
+
+    #[derive(imp::FromZeros)]
+    #[zerocopy(crate = "zerocopy_renamed")]
+    #[repr(i8)]
+    enum ImplicitNonFirstVariantIsZeroable {
+        A(::core::num::NonZeroU8) = 1,
+        B = -1,
+        C(bool),
+    }
+
+    util_assert_impl_all!(ImplicitNonFirstVariantIsZeroable: imp::FromZeros);
+}