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_attr.rs

@@ -0,0 +1,62 @@
+#![allow(clippy::let_underscore_untyped)]
+
+use paste::paste;
+use paste_test_suite::paste_test;
+
+#[test]
+fn test_attr() {
+    paste! {
+        #[paste_test(k = "val" "ue")]
+        struct A;
+
+        #[paste_test_suite::paste_test(k = "val" "ue")]
+        struct B;
+
+        #[::paste_test_suite::paste_test(k = "val" "ue")]
+        struct C;
+
+        #[paste_test(k = "va" [<l u>] e)]
+        struct D;
+    }
+
+    let _ = A;
+    let _ = B;
+    let _ = C;
+    let _ = D;
+}
+
+#[test]
+fn test_paste_cfg() {
+    macro_rules! m {
+        ($ret:ident, $width:expr) => {
+            paste! {
+                #[cfg(any(feature = "protocol_feature_" $ret:snake, target_pointer_width = "" $width))]
+                fn new() -> $ret { todo!() }
+            }
+        };
+    }
+
+    struct Paste;
+
+    #[cfg(target_pointer_width = "64")]
+    m!(Paste, 64);
+    #[cfg(target_pointer_width = "32")]
+    m!(Paste, 32);
+
+    let _ = new;
+}
+
+#[test]
+fn test_path_in_attr() {
+    macro_rules! m {
+        (#[x = $x:ty]) => {
+            stringify!($x)
+        };
+    }
+
+    let ty = paste! {
+        m!(#[x = foo::Bar])
+    };
+
+    assert_eq!("foo::Bar", ty);
+}