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/src/output_tests/expected/hash.expected.rs

@@ -0,0 +1,24 @@
+impl<T: Clone> ::zerocopy::util::macro_util::core_reexport::hash::Hash for Foo<T>
+where
+    Self: ::zerocopy::IntoBytes + ::zerocopy::Immutable,
+    Self: Sized,
+{
+    fn hash<H: ::zerocopy::util::macro_util::core_reexport::hash::Hasher>(
+        &self,
+        state: &mut H,
+    ) {
+        ::zerocopy::util::macro_util::core_reexport::hash::Hasher::write(
+            state,
+            ::zerocopy::IntoBytes::as_bytes(self),
+        )
+    }
+    fn hash_slice<H: ::zerocopy::util::macro_util::core_reexport::hash::Hasher>(
+        data: &[Self],
+        state: &mut H,
+    ) {
+        ::zerocopy::util::macro_util::core_reexport::hash::Hasher::write(
+            state,
+            ::zerocopy::IntoBytes::as_bytes(data),
+        )
+    }
+}