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/hash.rs

@@ -0,0 +1,39 @@
+// 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.
+
+// See comment in `include.rs` for why we disable the prelude.
+#![no_implicit_prelude]
+#![allow(warnings)]
+
+include!("include.rs");
+
+#[derive(imp::IntoBytes, imp::Immutable, imp::ByteHash)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+struct Struct {
+    a: u64,
+    b: u32,
+    c: u32,
+}
+
+util_assert_impl_all!(Struct: imp::IntoBytes, imp::hash::Hash);
+
+#[test]
+fn test_hash() {
+    use imp::{
+        hash::{Hash, Hasher},
+        DefaultHasher,
+    };
+    fn hash(val: impl Hash) -> u64 {
+        let mut hasher = DefaultHasher::new();
+        val.hash(&mut hasher);
+        hasher.finish()
+    }
+    hash(Struct { a: 10, b: 15, c: 20 });
+    hash(&[Struct { a: 10, b: 15, c: 20 }, Struct { a: 5, b: 4, c: 3 }]);
+}