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/embedded-graphics/benches/raw_data_iter.rs

@@ -0,0 +1,42 @@
+use criterion::*;
+use embedded_graphics::{iterator::raw::RawDataSlice, pixelcolor::raw::*};
+
+const TEST_DATA: &[u8] = include_bytes!("../fonts/src/10x20.bdf");
+
+macro_rules! impl_bench {
+    ($fn:ident, $type:ident) => {
+        fn $fn(c: &mut Criterion) {
+            c.bench_function(stringify!($type), |b| {
+                let slice = RawDataSlice::<$type, LittleEndian>::new(TEST_DATA);
+
+                b.iter(|| slice.into_iter().collect::<Vec<_>>())
+            });
+
+            c.bench_function(concat!(stringify!($type), " step by 20"), |b| {
+                let slice = RawDataSlice::<$type, LittleEndian>::new(TEST_DATA);
+
+                b.iter(|| slice.into_iter().step_by(20).collect::<Vec<_>>())
+            });
+        }
+    };
+}
+
+impl_bench!(raw_u1, RawU1);
+impl_bench!(raw_u2, RawU2);
+impl_bench!(raw_u4, RawU4);
+impl_bench!(raw_u8, RawU8);
+impl_bench!(raw_u16, RawU16);
+impl_bench!(raw_u24, RawU24);
+impl_bench!(raw_u32, RawU32);
+
+criterion_group!(
+    raw_data_iter,
+    raw_u1,
+    raw_u2,
+    raw_u4,
+    raw_u8,
+    raw_u16,
+    raw_u24,
+    raw_u32
+);
+criterion_main!(raw_data_iter);