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/winnow/examples/s_expression/main.rs

@@ -0,0 +1,20 @@
+//! In this example we build an [S-expression](https://en.wikipedia.org/wiki/S-expression)
+//! parser and tiny [lisp](https://en.wikipedia.org/wiki/Lisp_(programming_language)) interpreter.
+//! Lisp is a simple type of language made up of Atoms and Lists, forming easily parsable trees.
+
+#![cfg(feature = "alloc")]
+
+mod parser;
+
+fn main() {
+    let expression_1 = "((if (= (+ 3 (/ 9 3))
+         (* 2 3))
+     *
+     /)
+  456 123)";
+    println!(
+        "\"{}\"\nevaled gives us: {:?}",
+        expression_1,
+        parser::eval_from_str(expression_1)
+    );
+}