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/autocfg/src/tests.rs

@@ -0,0 +1,54 @@
+use std::path::Path;
+
+#[test]
+fn version_cmp() {
+    use super::version::Version;
+    let v123 = Version::new(1, 2, 3);
+
+    assert!(Version::new(1, 0, 0) < v123);
+    assert!(Version::new(1, 2, 2) < v123);
+    assert!(Version::new(1, 2, 3) == v123);
+    assert!(Version::new(1, 2, 4) > v123);
+    assert!(Version::new(1, 10, 0) > v123);
+    assert!(Version::new(2, 0, 0) > v123);
+}
+
+#[test]
+fn dir_does_not_contain_target() {
+    assert!(!super::dir_contains_target(
+        &Some("x86_64-unknown-linux-gnu".into()),
+        Path::new("/project/target/debug/build/project-ea75983148559682/out"),
+        None,
+    ));
+}
+
+#[test]
+fn dir_does_contain_target() {
+    assert!(super::dir_contains_target(
+        &Some("x86_64-unknown-linux-gnu".into()),
+        Path::new(
+            "/project/target/x86_64-unknown-linux-gnu/debug/build/project-0147aca016480b9d/out"
+        ),
+        None,
+    ));
+}
+
+#[test]
+fn dir_does_not_contain_target_with_custom_target_dir() {
+    assert!(!super::dir_contains_target(
+        &Some("x86_64-unknown-linux-gnu".into()),
+        Path::new("/project/custom/debug/build/project-ea75983148559682/out"),
+        Some("custom".into()),
+    ));
+}
+
+#[test]
+fn dir_does_contain_target_with_custom_target_dir() {
+    assert!(super::dir_contains_target(
+        &Some("x86_64-unknown-linux-gnu".into()),
+        Path::new(
+            "/project/custom/x86_64-unknown-linux-gnu/debug/build/project-0147aca016480b9d/out"
+        ),
+        Some("custom".into()),
+    ));
+}