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/semver/tests/regression.rs

@@ -0,0 +1,25 @@
+extern crate semver;
+extern crate crates_index;
+extern crate tempdir;
+
+// This test checks to see if every existing crate parses successfully. Important to not break the
+// Rust universe!
+
+#[cfg(feature = "ci")]
+#[test]
+fn test_regressions() {
+    use tempdir::TempDir;
+    use crates_index::Index;
+    use semver::Version;
+
+    let dir = TempDir::new("semver").unwrap();
+    let index = Index::new(dir.into_path());
+    index.clone().unwrap();
+
+    for krate in index.crates() {
+        for version in krate.versions() {
+            let v = version.version();
+            assert!(Version::parse(v).is_ok(), "failed: {} ({})", version.name(), v);
+        }
+    }
+}