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/ahash/tests/nopanic.rs

@@ -0,0 +1,81 @@
+use ahash::{AHasher, RandomState};
+use std::hash::{BuildHasher, Hash, Hasher};
+
+#[macro_use]
+extern crate no_panic;
+
+#[inline(never)]
+#[no_panic]
+fn hash_test_final(num: i32, string: &str) -> (u64, u64) {
+    use core::hash::Hasher;
+    let mut hasher1 = RandomState::with_seeds(1, 2, 3, 4).build_hasher();
+    let mut hasher2 = RandomState::with_seeds(3, 4, 5, 6).build_hasher();
+    hasher1.write_i32(num);
+    hasher2.write(string.as_bytes());
+    (hasher1.finish(), hasher2.finish())
+}
+
+#[inline(never)]
+fn hash_test_final_wrapper(num: i32, string: &str) {
+    hash_test_final(num, string);
+}
+
+struct SimpleBuildHasher {
+    hasher: AHasher,
+}
+
+impl SimpleBuildHasher {
+    fn hash_one<T: Hash>(&self, x: T) -> u64
+    where
+        Self: Sized,
+    {
+        let mut hasher = self.build_hasher();
+        x.hash(&mut hasher);
+        hasher.finish()
+    }
+}
+
+impl BuildHasher for SimpleBuildHasher {
+    type Hasher = AHasher;
+
+    fn build_hasher(&self) -> Self::Hasher {
+        self.hasher.clone()
+    }
+}
+
+#[inline(never)]
+#[no_panic]
+fn hash_test_specialize(num: i32, string: &str) -> (u64, u64) {
+    let hasher1 = RandomState::with_seeds(1, 2, 3, 4).build_hasher();
+    let hasher2 = RandomState::with_seeds(1, 2, 3, 4).build_hasher();
+    (
+        SimpleBuildHasher { hasher: hasher1 }.hash_one(num),
+        SimpleBuildHasher { hasher: hasher2 }.hash_one(string.as_bytes()),
+    )
+}
+
+#[inline(never)]
+fn hash_test_random_wrapper(num: i32, string: &str) {
+    hash_test_specialize(num, string);
+}
+
+#[inline(never)]
+#[no_panic]
+fn hash_test_random(num: i32, string: &str) -> (u64, u64) {
+    let build_hasher1 = RandomState::with_seeds(1, 2, 3, 4);
+    let build_hasher2 = RandomState::with_seeds(1, 2, 3, 4);
+    (build_hasher1.hash_one(&num), build_hasher2.hash_one(string.as_bytes()))
+}
+
+#[inline(never)]
+fn hash_test_specialize_wrapper(num: i32, string: &str) {
+    hash_test_specialize(num, string);
+}
+
+#[test]
+fn test_no_panic() {
+    hash_test_final_wrapper(2, "Foo");
+    hash_test_specialize_wrapper(2, "Bar");
+    hash_test_random(2, "Baz");
+    hash_test_random_wrapper(2, "Bat");
+}