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.rs

@@ -0,0 +1,34 @@
+// 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.
+
+// Many of our UI tests require the "derive" feature to function properly. In
+// particular:
+// - Some tests directly include `zerocopy-derive/tests/include.rs`, which
+//   derives traits on the `AU16` type.
+// - The file `invalid-impls.rs` directly includes `src/util/macros.rs` in order
+//   to test the `impl_or_verify!` macro which is defined in that file.
+//   Specifically, it tests the verification portion of that macro, which is
+//   enabled when `cfg(any(feature = "derive", test))`. While `--cfg test` is of
+//   course passed to the code in the file you're reading right now, `trybuild`
+//   does not pass `--cfg test` when it invokes Cargo. As a result, this
+//   `trybuild` test only tests the correct behavior when the "derive" feature
+//   is enabled.
+#![cfg(feature = "derive")]
+
+use testutil::UiTestRunner;
+
+#[test]
+#[cfg_attr(miri, ignore)]
+fn test_ui() {
+    // FIXME: Instead of manually passing `--features derive` when building, we
+    // should just pass whatever is passed to us.
+    UiTestRunner::new()
+        .rustc_arg("--cfg=feature=\"derive\"") // For tests that check #cfg(feature = "derive")
+        .rustc_arg("-Wwarnings") // To reflect typical user experience in stderr
+        .run();
+}