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/ui/union.rs

@@ -0,0 +1,134 @@
+// 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.
+
+#[macro_use]
+extern crate zerocopy_renamed;
+
+#[path = "../include.rs"]
+mod util;
+
+use std::mem::ManuallyDrop;
+
+use self::util::util::AU16;
+
+fn main() {}
+
+//
+// Immutable errors
+//
+
+#[derive(Immutable)]
+//~[msrv, stable, nightly]^ ERROR: the trait bound `UnsafeCell<()>: zerocopy_renamed::Immutable` is not satisfied
+#[zerocopy(crate = "zerocopy_renamed")]
+union Immutable1 {
+    a: ManuallyDrop<core::cell::UnsafeCell<()>>,
+}
+
+//
+// IntoBytes errors
+//
+
+#[derive(IntoBytes)]
+//~[msrv, stable, nightly]^ ERROR: unsupported on types with type parameters
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union IntoBytes1<T> {
+    foo: ManuallyDrop<T>,
+}
+
+#[derive(IntoBytes)]
+//~[msrv]^ ERROR: the trait bound `(): PaddingFree<IntoBytes2, 1_usize>` is not satisfied
+//~[stable, nightly]^^ ERROR: `IntoBytes2` has 1 total byte(s) of padding
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union IntoBytes2 {
+    foo: u8,
+    bar: [u8; 2],
+}
+
+// Need a `repr` attribute
+#[derive(IntoBytes)]
+//~[msrv, stable, nightly]^ ERROR: must be #[repr(C)], #[repr(packed)], or #[repr(transparent)]
+#[zerocopy(crate = "zerocopy_renamed")]
+union IntoBytes3 {
+    foo: u8,
+}
+
+// `repr(packed(2))` isn't equivalent to `repr(packed)`
+#[derive(IntoBytes)]
+//~[msrv, stable, nightly]^ ERROR: must be #[repr(C)], #[repr(packed)], or #[repr(transparent)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(packed(2))]
+union IntoBytes4 {
+    foo: u8,
+}
+
+//
+// Unaligned errors
+//
+
+#[derive(Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C, align(2))]
+//~[msrv, stable, nightly]^ ERROR: cannot derive `Unaligned` on type with alignment greater than 1
+union Unaligned1 {
+    foo: i16,
+    bar: AU16,
+}
+
+// Transparent unions are unstable; see issue #60405
+// <https://github.com/rust-lang/rust/issues/60405> for more information.
+
+// #[derive(Unaligned)]
+// #[repr(transparent, align(2))]
+// union Unaligned2 {
+//     foo: u8,
+// }
+
+#[derive(Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(packed, align(2))]
+//~[msrv, stable, nightly]^ ERROR: this conflicts with another representation hint
+union Unaligned3 {
+    //~[stable, nightly]^ ERROR: type has conflicting packed and align representation hints
+    foo: u8,
+}
+
+#[derive(Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(align(1), align(2))]
+//~[msrv, stable, nightly]^ ERROR: this conflicts with another representation hint
+struct Unaligned4 {
+    foo: u8,
+}
+
+#[derive(Unaligned)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(align(2), align(4))]
+//~[msrv, stable, nightly]^ ERROR: this conflicts with another representation hint
+struct Unaligned5 {
+    foo: u8,
+}
+
+#[derive(Unaligned)]
+//~[msrv, stable, nightly]^ ERROR: must have #[repr(C)], #[repr(transparent)], or #[repr(packed)] attribute in order to guarantee this type's alignment
+#[zerocopy(crate = "zerocopy_renamed")]
+union Unaligned6 {
+    foo: i16,
+    bar: AU16,
+}
+
+#[derive(Unaligned)]
+//~[msrv, stable, nightly]^ ERROR: must have #[repr(C)], #[repr(transparent)], or #[repr(packed)] attribute in order to guarantee this type's alignment
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(packed(2))]
+union Unaligned7 {
+    //~[stable, nightly]^ ERROR: packed type cannot transitively contain a `#[repr(align)]` type
+    foo: i16,
+    bar: AU16,
+}