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/arithmetic/test_parser.rs

@@ -0,0 +1,186 @@
+use snapbox::assert_data_eq;
+use snapbox::prelude::*;
+use snapbox::str;
+use winnow::prelude::*;
+
+use crate::parser::*;
+
+#[test]
+fn factor_test() {
+    let input = "3";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        3,
+    ),
+)
+
+"#]];
+    assert_data_eq!(factor.parse_peek(input).to_debug(), expected);
+
+    let input = " 12";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        12,
+    ),
+)
+
+"#]];
+    assert_data_eq!(factor.parse_peek(input).to_debug(), expected);
+
+    let input = "537 ";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        537,
+    ),
+)
+
+"#]];
+    assert_data_eq!(factor.parse_peek(input).to_debug(), expected);
+
+    let input = "  24     ";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        24,
+    ),
+)
+
+"#]];
+    assert_data_eq!(factor.parse_peek(input).to_debug(), expected);
+}
+
+#[test]
+fn term_test() {
+    let input = " 12 *2 /  3";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        8,
+    ),
+)
+
+"#]];
+    assert_data_eq!(term.parse_peek(input).to_debug(), expected);
+
+    let input = " 12 *2 /  3";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        8,
+    ),
+)
+
+"#]];
+    assert_data_eq!(term.parse_peek(input).to_debug(), expected);
+
+    let input = " 2* 3  *2 *2 /  3";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        8,
+    ),
+)
+
+"#]];
+    assert_data_eq!(term.parse_peek(input).to_debug(), expected);
+
+    let input = " 48 /  3/2";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        8,
+    ),
+)
+
+"#]];
+    assert_data_eq!(term.parse_peek(input).to_debug(), expected);
+}
+
+#[test]
+fn expr_test() {
+    let input = " 1 +  2 ";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        3,
+    ),
+)
+
+"#]];
+    assert_data_eq!(expr.parse_peek(input).to_debug(), expected);
+
+    let input = " 12 + 6 - 4+  3";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        17,
+    ),
+)
+
+"#]];
+    assert_data_eq!(expr.parse_peek(input).to_debug(), expected);
+
+    let input = " 1 + 2*3 + 4";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        11,
+    ),
+)
+
+"#]];
+    assert_data_eq!(expr.parse_peek(input).to_debug(), expected);
+}
+
+#[test]
+fn parens_test() {
+    let input = " (  2 )";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        2,
+    ),
+)
+
+"#]];
+    assert_data_eq!(expr.parse_peek(input).to_debug(), expected);
+
+    let input = " 2* (  3 + 4 ) ";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        14,
+    ),
+)
+
+"#]];
+    assert_data_eq!(expr.parse_peek(input).to_debug(), expected);
+
+    let input = "  2*2 / ( 5 - 1) + 3";
+    let expected = str![[r#"
+Ok(
+    (
+        "",
+        4,
+    ),
+)
+
+"#]];
+    assert_data_eq!(expr.parse_peek(input).to_debug(), expected);
+}