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/maybe-async-cfg/tests/ui/test_fail/01-empty-test.rs

@@ -0,0 +1,20 @@
+#[maybe_async_cfg::maybe(
+    sync(feature = "is_sync"), 
+)]
+async fn async_fn() -> bool {
+    true
+}
+
+#[maybe_async_cfg::maybe(
+    idents(async_fn(fn)),
+    sync(feature = "is_sync"), 
+    async(not(feature = "is_sync")),
+)]
+async fn test_async_fn() {
+    let res = async_fn().await;
+    assert_eq!(res, true);
+}
+
+fn main() {
+
+}

vendor/maybe-async-cfg/tests/ui/test_fail/01-empty-test.stderr

@@ -0,0 +1,5 @@
+error[E0425]: cannot find function `async_fn_async` in this scope
+  --> tests/ui/test_fail/01-empty-test.rs:14:15
+   |
+14 |     let res = async_fn().await;
+   |               ^^^^^^^^ not found in this scope

vendor/maybe-async-cfg/tests/ui/test_fail/02-unknown-path.rs

@@ -0,0 +1,21 @@
+#[maybe_async_cfg::maybe(
+    sync(feature = "is_sync"), 
+    unknown(not(feature = "is_sync")),
+)]
+async fn async_fn() -> bool {
+    true
+}
+
+#[maybe_async_cfg::maybe(
+    idents(async_fn(fn)),
+    sync(feature = "is_sync"), 
+    async(not(feature = "is_sync")),
+)]
+async fn test_async_fn() {
+    let res = async_fn().await;
+    assert_eq!(res, true);
+}
+
+fn main() {
+
+}

vendor/maybe-async-cfg/tests/ui/test_fail/02-unknown-path.stderr

@@ -0,0 +1,5 @@
+error[E0425]: cannot find function `async_fn_async` in this scope
+  --> tests/ui/test_fail/02-unknown-path.rs:15:15
+   |
+15 |     let res = async_fn().await;
+   |               ^^^^^^^^ not found in this scope

vendor/maybe-async-cfg/tests/ui/test_fail/03-async-gt2.rs

@@ -0,0 +1,23 @@
+#[maybe_async_cfg::maybe(
+    sync(feature = "is_sync"), 
+    async(not(feature = "is_sync")),
+)]
+async fn async_fn() -> bool {
+    true
+}
+
+//#[maybe_async::test(feature="is_sync", async(feature="async", async_std::test, added))]
+#[maybe_async_cfg::maybe(
+    idents(async_fn(fn)),
+    sync(feature = "is_sync"), 
+    async(not(feature = "is_sync")),
+    async(not(feature = "is_sync")),
+)]
+async fn test_async_fn() {
+    let res = async_fn().await;
+    assert_eq!(res, true);
+}
+
+fn main() {
+
+}

vendor/maybe-async-cfg/tests/ui/test_fail/03-async-gt2.stderr

@@ -0,0 +1,10 @@
+error[E0428]: the name `test_async_fn_async` is defined multiple times
+  --> tests/ui/test_fail/03-async-gt2.rs:16:1
+   |
+16 | async fn test_async_fn() {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+   | |
+   | `test_async_fn_async` redefined here
+   | previous definition of the value `test_async_fn_async` here
+   |
+   = note: `test_async_fn_async` must be defined only once in the value namespace of this module

vendor/maybe-async-cfg/tests/ui/test_fail/04-bad-sync-cond.rs

@@ -0,0 +1,23 @@
+#[maybe_async_cfg::maybe(
+    sync(feature = "is_sync"), 
+    async(not(feature = "is_sync")),
+)]
+async fn async_fn() -> bool {
+    true
+}
+
+// bad sync condition
+//#[maybe_async::test(unknown(feature="async", async_std::test))]
+#[maybe_async_cfg::maybe(
+    idents(async_fn(fn)),
+    sync(unknown = "is_sync"), 
+    async(not(feature = "is_sync")),
+)]
+async fn test_async_fn() {
+    let res = async_fn().await;
+    assert_eq!(res, true);
+}
+
+fn main() {
+
+}

vendor/maybe-async-cfg/tests/ui/test_fail/04-bad-sync-cond.stderr

@@ -0,0 +1,5 @@
+error: Wrong name for name-value pair: unknown
+  --> tests/ui/test_fail/04-bad-sync-cond.rs:13:10
+   |
+13 |     sync(unknown = "is_sync"),
+   |          ^^^^^^^^^^^^^^^^^^^