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/framebuffer.rs

@@ -0,0 +1,112 @@
+use criterion::*;
+use embedded_graphics::{
+    framebuffer::{buffer_size, Framebuffer},
+    geometry::Point,
+    image::GetPixel,
+    pixelcolor::{raw::LittleEndian, BinaryColor, Rgb565},
+    prelude::{DrawTarget, Size, WebColors},
+    primitives::{Primitive, PrimitiveStyle, Rectangle},
+};
+
+fn framebuffer_set_1bpp(c: &mut Criterion) {
+    c.bench_function("framebuffer set pixel 1bpp", |b| {
+        let mut fb = Framebuffer::<
+            BinaryColor,
+            _,
+            LittleEndian,
+            320,
+            240,
+            { buffer_size::<BinaryColor>(320, 240) },
+        >::new();
+
+        b.iter(|| {
+            fb.set_pixel(Point::new(1, 1), BinaryColor::On);
+            fb.set_pixel(Point::new(300, 200), BinaryColor::On);
+        })
+    });
+}
+
+fn framebuffer_get_1bpp(c: &mut Criterion) {
+    c.bench_function("framebuffer get pixel 1bpp", |b| {
+        let fb = Framebuffer::<
+            BinaryColor,
+            _,
+            LittleEndian,
+            320,
+            240,
+            { buffer_size::<BinaryColor>(320, 240) },
+        >::new();
+
+        b.iter(|| {
+            fb.pixel(Point::new(1, 1));
+            fb.pixel(Point::new(300, 200));
+        })
+    });
+}
+
+fn framebuffer_1bpp_draw_iter(c: &mut Criterion) {
+    c.bench_function("framebuffer 1bpp draw iter", |b| {
+        let mut fb = Framebuffer::<
+            BinaryColor,
+            _,
+            LittleEndian,
+            320,
+            240,
+            { buffer_size::<BinaryColor>(320, 240) },
+        >::new();
+
+        b.iter(|| {
+            let rect = Rectangle::new(Point::new(20, 30), Size::new(40, 50))
+                .into_styled(PrimitiveStyle::with_fill(BinaryColor::On))
+                .pixels();
+
+            fb.draw_iter(rect).unwrap();
+        })
+    });
+}
+
+fn framebuffer_set_rgb565(c: &mut Criterion) {
+    c.bench_function("framebuffer set pixel rgb565", |b| {
+        let mut fb = Framebuffer::<
+            Rgb565,
+            _,
+            LittleEndian,
+            320,
+            240,
+            { buffer_size::<Rgb565>(320, 240) },
+        >::new();
+
+        b.iter(|| {
+            fb.set_pixel(Point::new(1, 1), Rgb565::CSS_DARK_SALMON);
+            fb.set_pixel(Point::new(300, 200), Rgb565::CSS_TEAL);
+        })
+    });
+}
+
+fn framebuffer_get_rgb565(c: &mut Criterion) {
+    c.bench_function("framebuffer get pixel rgb565", |b| {
+        let fb = Framebuffer::<
+            Rgb565,
+            _,
+            LittleEndian,
+            320,
+            240,
+            { buffer_size::<Rgb565>(320, 240) },
+        >::new();
+
+        b.iter(|| {
+            fb.pixel(Point::new(1, 1));
+            fb.pixel(Point::new(300, 200));
+        })
+    });
+}
+
+criterion_group!(
+    framebuffer,
+    framebuffer_set_1bpp,
+    framebuffer_get_1bpp,
+    framebuffer_set_rgb565,
+    framebuffer_get_rgb565,
+    framebuffer_1bpp_draw_iter
+);
+criterion_main!(framebuffer);