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/tests/ui/try_transmute_ref.rs

@@ -0,0 +1,36 @@
+// Copyright 2024 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.
+
+include!("../include.rs");
+
+use util::{NotZerocopy, AU16};
+use zerocopy::try_transmute_ref;
+
+fn main() {}
+
+fn ref_dst_mutable() {
+    // `try_transmute_ref!` requires that its destination type be an immutable
+    // reference.
+    let _: Result<&mut u8, _> = try_transmute_ref!(&0u8);
+    //~[msrv, stable, nightly]^ ERROR: mismatched types
+    //~[msrv, stable, nightly]^^ ERROR: mismatched types
+
+    // `try_transmute_ref` requires that the source type implements `Immutable`
+    // and `IntoBytes`
+    let dst_not_try_from_bytes: Result<&NotZerocopy, _> = try_transmute_ref!(&AU16(0));
+    //~[msrv, stable, nightly]^ ERROR: the trait bound `NotZerocopy: TryFromBytes` is not satisfied
+    //~[msrv, stable, nightly]^^ ERROR: the trait bound `NotZerocopy: TryFromBytes` is not satisfied
+    //~[msrv, stable, nightly]^^^ ERROR: the trait bound `NotZerocopy: TryFromBytes` is not satisfied
+    //~[msrv, stable, nightly]^^^^ ERROR: the trait bound `NotZerocopy: Immutable` is not satisfied
+
+    // `try_transmute_ref` requires that the source type implements `Immutable`
+    // and `IntoBytes`
+    let src_not_into_bytes: Result<&AU16, _> = try_transmute_ref!(&NotZerocopy(AU16(0)));
+    //~[msrv, stable, nightly]^ ERROR: the trait bound `NotZerocopy<AU16>: IntoBytes` is not satisfied
+    //~[msrv, stable, nightly]^^ ERROR: the trait bound `NotZerocopy<AU16>: Immutable` is not satisfied
+}