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/transmute.rs

@@ -0,0 +1,22 @@
+// Copyright 2022 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::transmute;
+
+fn main() {}
+
+// `transmute` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+//~[msrv, stable, nightly]^ ERROR: the trait bound `NotZerocopy: FromBytes` is not satisfied
+
+// `transmute` requires that the source type implements `IntoBytes`
+const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+//~[msrv, stable, nightly]^ ERROR: the trait bound `NotZerocopy<AU16>: IntoBytes` is not satisfied