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/syn-1.0.109/tests/test_should_parse.rs

@@ -0,0 +1,45 @@
+macro_rules! should_parse {
+    ($name:ident, { $($in:tt)* }) => {
+        #[test]
+        fn $name() {
+            // Make sure we can parse the file!
+            syn::parse_file(stringify!($($in)*)).unwrap();
+        }
+    }
+}
+
+should_parse!(generic_associated_type, {
+    impl Foo {
+        type Item = &'a i32;
+        fn foo<'a>(&'a self) -> Self::Item<'a> {}
+    }
+});
+
+#[rustfmt::skip]
+should_parse!(const_generics_use, {
+    type X = Foo<5>;
+    type Y = Foo<"foo">;
+    type Z = Foo<X>;
+    type W = Foo<{ X + 10 }>;
+});
+
+should_parse!(trailing_plus_type, {
+    type A = Box<Foo>;
+    type A = Box<Foo + 'a>;
+    type A = Box<'a + Foo>;
+});
+
+should_parse!(generic_associated_type_where, {
+    trait Foo {
+        type Item;
+        fn foo<T>(&self, t: T) -> Self::Item<T>;
+    }
+});
+
+should_parse!(match_with_block_expr, {
+    fn main() {
+        match false {
+            _ => {}.a(),
+        }
+    }
+});