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/tests/regression/issue1108.rs

@@ -0,0 +1,5 @@
+#[test]
+fn issue1108() {
+    let data = "impl<x<>>::x for";
+    let _ = syn::parse_file(data);
+}

vendor/syn/tests/regression/issue1235.rs

@@ -0,0 +1,32 @@
+use proc_macro2::{Delimiter, Group};
+use quote::quote;
+
+#[test]
+fn main() {
+    // Okay. Rustc allows top-level `static` with no value syntactically, but
+    // not semantically. Syn parses as Item::Verbatim.
+    let tokens = quote! {
+        pub static FOO: usize;
+        pub static BAR: usize;
+    };
+    let file = syn::parse2::<syn::File>(tokens).unwrap();
+    println!("{:#?}", file);
+
+    // Okay.
+    let inner = Group::new(
+        Delimiter::None,
+        quote!(static FOO: usize = 0; pub static BAR: usize = 0),
+    );
+    let tokens = quote!(pub #inner;);
+    let file = syn::parse2::<syn::File>(tokens).unwrap();
+    println!("{:#?}", file);
+
+    // Formerly parser crash.
+    let inner = Group::new(
+        Delimiter::None,
+        quote!(static FOO: usize; pub static BAR: usize),
+    );
+    let tokens = quote!(pub #inner;);
+    let file = syn::parse2::<syn::File>(tokens).unwrap();
+    println!("{:#?}", file);
+}