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/winnow/examples/json/bench.rs

@@ -0,0 +1,78 @@
+use winnow::prelude::*;
+use winnow::Partial;
+
+mod json;
+mod parser_alt;
+mod parser_dispatch;
+mod parser_partial;
+
+fn json_bench(c: &mut criterion::Criterion) {
+    let data = [("small", SMALL), ("canada", CANADA)];
+    let mut group = c.benchmark_group("json");
+    for (name, sample) in data {
+        let len = sample.len();
+        group.throughput(criterion::Throughput::Bytes(len as u64));
+
+        group.bench_with_input(
+            criterion::BenchmarkId::new("dispatch", name),
+            &len,
+            |b, _| {
+                type Error = winnow::error::ErrMode<winnow::error::ContextError>;
+
+                b.iter(|| parser_dispatch::json::<Error>.parse_peek(sample).unwrap());
+            },
+        );
+        group.bench_with_input(
+            criterion::BenchmarkId::new("modeless", name),
+            &len,
+            |b, _| {
+                type Error = winnow::error::ContextError;
+
+                b.iter(|| parser_dispatch::json::<Error>.parse_peek(sample).unwrap());
+            },
+        );
+        group.bench_with_input(
+            criterion::BenchmarkId::new("empty-error", name),
+            &len,
+            |b, _| {
+                type Error<'i> = winnow::error::EmptyError;
+
+                b.iter(|| {
+                    parser_dispatch::json::<Error<'_>>
+                        .parse_peek(sample)
+                        .unwrap()
+                });
+            },
+        );
+        group.bench_with_input(criterion::BenchmarkId::new("alt", name), &len, |b, _| {
+            type Error = winnow::error::ContextError;
+
+            b.iter(|| parser_alt::json::<Error>.parse_peek(sample).unwrap());
+        });
+        group.bench_with_input(
+            criterion::BenchmarkId::new("streaming", name),
+            &len,
+            |b, _| {
+                type Error = winnow::error::ContextError;
+
+                b.iter(|| {
+                    parser_partial::json::<Error>
+                        .parse_peek(Partial::new(sample))
+                        .unwrap()
+                });
+            },
+        );
+    }
+    group.finish();
+}
+
+const SMALL: &str = "  { \"a\"\t: 42,
+  \"b\": [ \"x\", \"y\", 12 ,\"\\u2014\", \"\\uD83D\\uDE10\"] ,
+  \"c\": { \"hello\" : \"world\"
+  }
+  }  ";
+
+const CANADA: &str = include_str!("../../third_party/nativejson-benchmark/data/canada.json");
+
+criterion::criterion_group!(benches, json_bench,);
+criterion::criterion_main!(benches);