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/enum-as-inner/tests/basic.rs

@@ -0,0 +1,90 @@
+#![warn(
+    clippy::default_trait_access,
+    clippy::dbg_macro,
+    clippy::print_stdout,
+    clippy::unimplemented,
+    clippy::use_self,
+    missing_copy_implementations,
+    missing_docs,
+    non_snake_case,
+    non_upper_case_globals,
+    rust_2018_idioms,
+    unreachable_pub
+)]
+
+use enum_as_inner::EnumAsInner;
+
+pub mod name_collisions {
+    #![allow(dead_code, missing_copy_implementations, missing_docs)]
+    pub struct Option;
+    pub struct Some;
+    pub struct None;
+    pub struct Result;
+    pub struct Ok;
+    pub struct Err;
+}
+#[allow(unused_imports)]
+use name_collisions::*;
+
+#[derive(Debug, EnumAsInner)]
+enum EmptyTest {}
+
+#[test]
+fn test_empty() {
+    let empty = std::option::Option::None::<EmptyTest>;
+
+    assert!(empty.is_none());
+}
+
+#[derive(Debug, EnumAsInner)]
+enum EmptyParendsTest {
+    Empty(),
+}
+
+#[test]
+fn test_empty_parends() {
+    let mut empty = EmptyParendsTest::Empty();
+
+    assert!(empty.is_empty());
+
+    empty
+        .as_empty()
+        .expect("should have been something and a unit");
+    empty
+        .as_empty_mut()
+        .expect("should have been something and a unit");
+
+    empty
+        .into_empty()
+        .expect("should have been something and a unit");
+}
+
+#[derive(Debug, EnumAsInner)]
+enum OneTest {
+    One(u32),
+}
+
+#[test]
+fn test_one() {
+    let mut empty = OneTest::One(1);
+
+    assert!(empty.is_one());
+    assert_eq!(*empty.as_one().unwrap(), 1);
+    assert_eq!(*empty.as_one_mut().unwrap(), 1);
+    assert_eq!(empty.into_one().unwrap(), 1);
+}
+
+#[derive(Debug, EnumAsInner)]
+enum MultiTest {
+    Multi(u32, u32),
+}
+
+#[test]
+fn test_multi() {
+    let mut multi = MultiTest::Multi(1, 1);
+
+    assert!(multi.is_multi());
+    assert_eq!(multi.as_multi().unwrap(), (&1_u32, &1_u32));
+    assert_eq!(multi.as_multi_mut().unwrap(), (&mut 1_u32, &mut 1_u32));
+    assert_eq!(multi.into_multi().unwrap(), (1_u32, 1_u32));
+}