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.rs

@@ -0,0 +1,27 @@
+// 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.
+
+use testutil::UiTestRunner;
+
+#[test]
+#[cfg_attr(miri, ignore)]
+fn ui() {
+    // This tests the behavior when `--cfg zerocopy_derive_union_into_bytes` is
+    // present.
+    UiTestRunner::new()
+        .rustc_arg("--cfg=zerocopy_derive_union_into_bytes")
+        .rustc_arg("--cfg=zerocopy_unstable_derive_on_error")
+        .rustc_arg("-Wwarnings") // To ensure .stderr files reflect typical user encounter
+        .run();
+
+    // This tests the behavior when various `--cfg` flags are not present.
+    UiTestRunner::new()
+        .subdir("cfgs")
+        .rustc_arg("-Wwarnings") // To ensure .stderr files reflect typical user encounter
+        .run();
+}