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_to_bytes.rs

@@ -0,0 +1,156 @@
+// 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");
+
+// An enum is `IntoBytes` if if has a defined repr.
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+enum C {
+    A,
+}
+
+util_assert_impl_all!(C: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u8)]
+enum U8 {
+    A,
+}
+
+util_assert_impl_all!(U8: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u16)]
+enum U16 {
+    A,
+}
+
+util_assert_impl_all!(U16: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u32)]
+enum U32 {
+    A,
+}
+
+util_assert_impl_all!(U32: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u64)]
+enum U64 {
+    A,
+}
+
+util_assert_impl_all!(U64: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(usize)]
+enum Usize {
+    A,
+}
+
+util_assert_impl_all!(Usize: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(i8)]
+enum I8 {
+    A,
+}
+
+util_assert_impl_all!(I8: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(i16)]
+enum I16 {
+    A,
+}
+
+util_assert_impl_all!(I16: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(i32)]
+enum I32 {
+    A,
+}
+
+util_assert_impl_all!(I32: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(i64)]
+enum I64 {
+    A,
+}
+
+util_assert_impl_all!(I64: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(isize)]
+enum Isize {
+    A,
+}
+
+util_assert_impl_all!(Isize: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u8)]
+enum HasData {
+    A(u8),
+    B(i8),
+}
+
+util_assert_impl_all!(HasData: imp::IntoBytes);
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u32)]
+enum HasData32 {
+    A(u32),
+    B(i32),
+    C([u8; 4]),
+    D([u16; 2]),
+}
+
+util_assert_impl_all!(HasData: imp::IntoBytes);
+
+// After #1752 landed but before #1758 was fixed, this failed to compile because
+// the padding check treated the tag type as being `#[repr(u8, align(2))] struct
+// Tag { A }`, which is two bytes long, rather than the correct `#[repr(u8)]
+// struct Tag { A }`, which is one byte long.
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u8, align(2))]
+enum BadTagWouldHavePadding {
+    A(u8, u16),
+}
+
+#[derive(imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(u8, align(2))]
+enum HasAlign {
+    A(u8),
+}
+
+util_assert_impl_all!(HasAlign: imp::IntoBytes);