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_pat.rs

@@ -0,0 +1,67 @@
+#[macro_use]
+mod macros;
+
+use proc_macro2::{Delimiter, Group, TokenStream, TokenTree};
+use quote::quote;
+use std::iter::FromIterator;
+use syn::{Item, Pat, Stmt};
+
+#[test]
+fn test_pat_ident() {
+    match syn::parse2(quote!(self)).unwrap() {
+        Pat::Ident(_) => (),
+        value => panic!("expected PatIdent, got {:?}", value),
+    }
+}
+
+#[test]
+fn test_pat_path() {
+    match syn::parse2(quote!(self::CONST)).unwrap() {
+        Pat::Path(_) => (),
+        value => panic!("expected PatPath, got {:?}", value),
+    }
+}
+
+#[test]
+fn test_leading_vert() {
+    // https://github.com/rust-lang/rust/blob/1.43.0/src/test/ui/or-patterns/remove-leading-vert.rs
+
+    syn::parse_str::<Item>("fn f() {}").unwrap();
+    syn::parse_str::<Item>("fn fun1(| A: E) {}").unwrap_err();
+    syn::parse_str::<Item>("fn fun2(|| A: E) {}").unwrap_err();
+
+    syn::parse_str::<Stmt>("let | () = ();").unwrap();
+    syn::parse_str::<Stmt>("let (| A): E;").unwrap();
+    syn::parse_str::<Stmt>("let (|| A): (E);").unwrap_err();
+    syn::parse_str::<Stmt>("let (| A,): (E,);").unwrap();
+    syn::parse_str::<Stmt>("let [| A]: [E; 1];").unwrap();
+    syn::parse_str::<Stmt>("let [|| A]: [E; 1];").unwrap_err();
+    syn::parse_str::<Stmt>("let TS(| A): TS;").unwrap();
+    syn::parse_str::<Stmt>("let TS(|| A): TS;").unwrap_err();
+    syn::parse_str::<Stmt>("let NS { f: | A }: NS;").unwrap();
+    syn::parse_str::<Stmt>("let NS { f: || A }: NS;").unwrap_err();
+}
+
+#[test]
+fn test_group() {
+    let group = Group::new(Delimiter::None, quote!(Some(_)));
+    let tokens = TokenStream::from_iter(vec![TokenTree::Group(group)]);
+
+    snapshot!(tokens as Pat, @r###"
+    Pat::TupleStruct {
+        path: Path {
+            segments: [
+                PathSegment {
+                    ident: "Some",
+                    arguments: None,
+                },
+            ],
+        },
+        pat: PatTuple {
+            elems: [
+                Pat::Wild,
+            ],
+        },
+    }
+    "###);
+}