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/paste/tests/test_doc.rs

@@ -0,0 +1,79 @@
+#![allow(clippy::let_underscore_untyped)]
+
+use paste::paste;
+
+#[test]
+fn test_paste_doc() {
+    macro_rules! m {
+        ($ret:ident) => {
+            paste! {
+                #[doc = "Create a new [`" $ret "`] object."]
+                fn new() -> $ret { todo!() }
+            }
+        };
+    }
+
+    struct Paste;
+    m!(Paste);
+
+    let _ = new;
+}
+
+macro_rules! get_doc {
+    (#[doc = $literal:tt]) => {
+        $literal
+    };
+}
+
+#[test]
+fn test_escaping() {
+    let doc = paste! {
+        get_doc!(#[doc = "s\"" r#"r#""#])
+    };
+
+    let expected = "s\"r#\"";
+    assert_eq!(doc, expected);
+}
+
+#[test]
+fn test_literals() {
+    let doc = paste! {
+        get_doc!(#[doc = "int=" 0x1 " bool=" true " float=" 0.01])
+    };
+
+    let expected = "int=0x1 bool=true float=0.01";
+    assert_eq!(doc, expected);
+}
+
+#[test]
+fn test_case() {
+    let doc = paste! {
+        get_doc!(#[doc = "HTTP " get:upper "!"])
+    };
+
+    let expected = "HTTP GET!";
+    assert_eq!(doc, expected);
+}
+
+// https://github.com/dtolnay/paste/issues/63
+#[test]
+fn test_stringify() {
+    macro_rules! create {
+        ($doc:expr) => {
+            paste! {
+                #[doc = $doc]
+                pub struct Struct;
+            }
+        };
+    }
+
+    macro_rules! forward {
+        ($name:ident) => {
+            create!(stringify!($name));
+        };
+    }
+
+    forward!(documentation);
+
+    let _ = Struct;
+}