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/num-traits/src/macros.rs

@@ -0,0 +1,44 @@
+// not all are used in all features configurations
+#![allow(unused)]
+
+/// Forward a method to an inherent method or a base trait method.
+macro_rules! forward {
+    ($( Self :: $method:ident ( self $( , $arg:ident : $ty:ty )* ) -> $ret:ty ; )*)
+        => {$(
+            #[inline]
+            fn $method(self $( , $arg : $ty )* ) -> $ret {
+                Self::$method(self $( , $arg )* )
+            }
+        )*};
+    ($( $base:ident :: $method:ident ( self $( , $arg:ident : $ty:ty )* ) -> $ret:ty ; )*)
+        => {$(
+            #[inline]
+            fn $method(self $( , $arg : $ty )* ) -> $ret {
+                <Self as $base>::$method(self $( , $arg )* )
+            }
+        )*};
+    ($( $base:ident :: $method:ident ( $( $arg:ident : $ty:ty ),* ) -> $ret:ty ; )*)
+        => {$(
+            #[inline]
+            fn $method( $( $arg : $ty ),* ) -> $ret {
+                <Self as $base>::$method( $( $arg ),* )
+            }
+        )*};
+    ($( $imp:path as $method:ident ( self $( , $arg:ident : $ty:ty )* ) -> $ret:ty ; )*)
+        => {$(
+            #[inline]
+            fn $method(self $( , $arg : $ty )* ) -> $ret {
+                $imp(self $( , $arg )* )
+            }
+        )*};
+}
+
+macro_rules! constant {
+    ($( $method:ident () -> $ret:expr ; )*)
+        => {$(
+            #[inline]
+            fn $method() -> Self {
+                $ret
+            }
+        )*};
+}