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/litrs-0.4.2/src/bool/mod.rs

@@ -0,0 +1,55 @@
+use std::fmt;
+
+use crate::{ParseError, err::{perr, ParseErrorKind::*}};
+
+
+/// A bool literal: `true` or `false`. Also see [the reference][ref].
+///
+/// Notice that, strictly speaking, from Rust point of view "boolean literals" are not
+/// actual literals but [keywords].
+///
+/// [ref]: https://doc.rust-lang.org/reference/expressions/literal-expr.html#boolean-literal-expressions
+/// [keywords]: https://doc.rust-lang.org/reference/keywords.html#strict-keywords
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BoolLit {
+    False,
+    True,
+}
+
+impl BoolLit {
+    /// Parses the input as a bool literal. Returns an error if the input is
+    /// invalid or represents a different kind of literal.
+    pub fn parse(s: &str) -> Result<Self, ParseError> {
+        match s {
+            "false" => Ok(Self::False),
+            "true" => Ok(Self::True),
+            _ => Err(perr(None, InvalidLiteral)),
+        }
+    }
+
+    /// Returns the actual Boolean value of this literal.
+    pub fn value(self) -> bool {
+        match self {
+            Self::False => false,
+            Self::True => true,
+        }
+    }
+
+    /// Returns the literal as string.
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::False => "false",
+            Self::True => "true",
+        }
+    }
+}
+
+impl fmt::Display for BoolLit {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad(self.as_str())
+    }
+}
+
+
+#[cfg(test)]
+mod tests;

vendor/litrs-0.4.2/src/bool/tests.rs

@@ -0,0 +1,48 @@
+use crate::{
+    Literal, BoolLit,
+    test_util::assert_parse_ok_eq,
+};
+
+macro_rules! assert_bool_parse {
+    ($input:literal, $expected:expr) => {
+        assert_parse_ok_eq(
+            $input, Literal::parse($input), Literal::Bool($expected), "Literal::parse");
+        assert_parse_ok_eq($input, BoolLit::parse($input), $expected, "BoolLit::parse");
+    };
+}
+
+
+
+#[test]
+fn parse_ok() {
+    assert_bool_parse!("false", BoolLit::False);
+    assert_bool_parse!("true", BoolLit::True);
+}
+
+#[test]
+fn parse_err() {
+    assert!(Literal::parse("fa").is_err());
+    assert!(Literal::parse("fal").is_err());
+    assert!(Literal::parse("fals").is_err());
+    assert!(Literal::parse(" false").is_err());
+    assert!(Literal::parse("false ").is_err());
+    assert!(Literal::parse("False").is_err());
+
+    assert!(Literal::parse("tr").is_err());
+    assert!(Literal::parse("tru").is_err());
+    assert!(Literal::parse(" true").is_err());
+    assert!(Literal::parse("true ").is_err());
+    assert!(Literal::parse("True").is_err());
+}
+
+#[test]
+fn value() {
+    assert!(!BoolLit::False.value());
+    assert!(BoolLit::True.value());
+}
+
+#[test]
+fn as_str() {
+    assert_eq!(BoolLit::False.as_str(), "false");
+    assert_eq!(BoolLit::True.as_str(), "true");
+}