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/ini/main.rs

@@ -0,0 +1,60 @@
+use winnow::prelude::*;
+
+mod parser;
+mod parser_str;
+
+fn main() -> Result<(), lexopt::Error> {
+    let args = Args::parse()?;
+
+    let input = args.input.as_deref().unwrap_or("1 + 1");
+
+    if args.binary {
+        match parser::categories.parse(input.as_bytes()) {
+            Ok(result) => {
+                println!("  {result:?}");
+            }
+            Err(err) => {
+                println!("  {err:?}");
+            }
+        }
+    } else {
+        match parser_str::categories.parse(input) {
+            Ok(result) => {
+                println!("  {result:?}");
+            }
+            Err(err) => {
+                println!("  {err}");
+            }
+        }
+    }
+
+    Ok(())
+}
+
+#[derive(Default)]
+struct Args {
+    input: Option<String>,
+    binary: bool,
+}
+
+impl Args {
+    fn parse() -> Result<Self, lexopt::Error> {
+        use lexopt::prelude::*;
+
+        let mut res = Args::default();
+
+        let mut args = lexopt::Parser::from_env();
+        while let Some(arg) = args.next()? {
+            match arg {
+                Long("binary") => {
+                    res.binary = true;
+                }
+                Value(input) => {
+                    res.input = Some(input.string()?);
+                }
+                _ => return Err(arg.unexpected()),
+            }
+        }
+        Ok(res)
+    }
+}