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/hashbrown/benches/with_capacity.rs

@@ -0,0 +1,38 @@
+#![feature(test)]
+
+extern crate test;
+
+use hashbrown::HashMap;
+use test::{black_box, Bencher};
+
+type Map<K, V> = HashMap<K, V>;
+
+macro_rules! bench_with_capacity {
+    ($name:ident, $cap:expr) => {
+        #[bench]
+        fn $name(b: &mut Bencher) {
+            b.iter(|| {
+                // Construct a new empty map with a given capacity and return it to avoid
+                // being optimized away. Dropping it measures allocation + minimal setup.
+                let m: Map<usize, usize> = Map::with_capacity($cap);
+                black_box(m)
+            });
+        }
+    };
+}
+
+bench_with_capacity!(with_capacity_000000, 0);
+bench_with_capacity!(with_capacity_000001, 1);
+bench_with_capacity!(with_capacity_000003, 3);
+bench_with_capacity!(with_capacity_000007, 7);
+bench_with_capacity!(with_capacity_000008, 8);
+bench_with_capacity!(with_capacity_000016, 16);
+bench_with_capacity!(with_capacity_000032, 32);
+bench_with_capacity!(with_capacity_000064, 64);
+bench_with_capacity!(with_capacity_000128, 128);
+bench_with_capacity!(with_capacity_000256, 256);
+bench_with_capacity!(with_capacity_000512, 512);
+bench_with_capacity!(with_capacity_001024, 1024);
+bench_with_capacity!(with_capacity_004096, 4096);
+bench_with_capacity!(with_capacity_016384, 16384);
+bench_with_capacity!(with_capacity_065536, 65536);