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/msrv_specific.rs

@@ -0,0 +1,40 @@
+// 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.
+
+// This file contains tests which trigger errors on MSRV during a different
+// compiler pass compared to the stable or nightly toolchains.
+
+#[macro_use]
+extern crate zerocopy_renamed;
+
+#[path = "../include.rs"]
+mod util;
+
+use zerocopy_renamed::IntoBytes;
+
+use self::util::util::AU16;
+
+fn main() {}
+
+// `repr(C, packed(2))` is not equivalent to `repr(C, packed)`.
+#[derive(IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C, packed(2))]
+struct IntoBytes1<T> {
+    t0: T,
+    // Add a second field to avoid triggering the "repr(C) struct with one
+    // field" special case.
+    t1: T,
+}
+
+fn is_into_bytes_1<T: IntoBytes>() {
+    if false {
+        is_into_bytes_1::<IntoBytes1<AU16>>();
+        //~[msrv, stable, nightly]^ ERROR: the trait bound `AU16: zerocopy_renamed::Unaligned` is not satisfied
+    }
+}