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/issue_2835.rs

@@ -0,0 +1,23 @@
+// Copyright 2025 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 zerocopy_renamed::{IntoBytes, Unalign};
+
+#[allow(unused)]
+#[derive(IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct Struct {
+    leading: Unalign<u32>,
+    trailing: [u8],
+}
+
+#[test]
+fn test_issue_2835() {
+    // Compilation is enough to verify the fix
+}