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/thiserror/tests/test_from.rs

@@ -0,0 +1,64 @@
+#![allow(clippy::extra_unused_type_parameters)]
+
+use std::io;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub struct ErrorStruct {
+    #[from]
+    source: io::Error,
+}
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub struct ErrorStructOptional {
+    #[from]
+    source: Option<io::Error>,
+}
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub struct ErrorTuple(#[from] io::Error);
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub struct ErrorTupleOptional(#[from] Option<io::Error>);
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub enum ErrorEnum {
+    Test {
+        #[from]
+        source: io::Error,
+    },
+}
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub enum ErrorEnumOptional {
+    Test {
+        #[from]
+        source: Option<io::Error>,
+    },
+}
+
+#[derive(Error, Debug)]
+#[error("...")]
+pub enum Many {
+    Any(#[from] anyhow::Error),
+    Io(#[from] io::Error),
+}
+
+fn assert_impl<T: From<io::Error>>() {}
+
+#[test]
+fn test_from() {
+    assert_impl::<ErrorStruct>();
+    assert_impl::<ErrorStructOptional>();
+    assert_impl::<ErrorTuple>();
+    assert_impl::<ErrorTupleOptional>();
+    assert_impl::<ErrorEnum>();
+    assert_impl::<ErrorEnumOptional>();
+    assert_impl::<Many>();
+}