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/src/debug.rs

@@ -0,0 +1,80 @@
+#[cfg(feature="debug")]
+pub mod inner {
+
+    use proc_macro::TokenStream;
+    use proc_macro2::TokenStream as TokenStream2;
+    
+    use crate::params::MacroParameters;
+    
+    ////////////////////////////////////////////////////////////////////////////////////////////////
+    
+    pub fn dump_maybe(args: &TokenStream, input: &TokenStream) {
+        println!("--vvv------------------------------------------");
+        println!("maybe:");
+        println!("args:");
+        println!("{}", args);
+        println!("input:");
+        println!("{}", input);
+        println!("--^^^------------------------------------------");
+        println!("");
+    }
+
+    pub fn dump_tokens(name: &str, ts: &TokenStream) {
+        println!("--vvv------------------------------------------");
+        println!("{}:", name);
+        println!("{}", ts);
+        println!("--^^^------------------------------------------");
+        println!("");
+    }
+
+    pub fn dump_tokens2(name: &str, ts: &TokenStream2) {
+        println!("--vvv------------------------------------------");
+        println!("{}:", name);
+        println!("{}", ts);
+        println!("--^^^------------------------------------------");
+        println!("");
+    }
+    
+    pub fn dump_params(name: &str, params: &MacroParameters) {
+        println!("--vvv------------------------------------------");
+        println!("{}:", name);
+        println!("{:#?}", params);
+        println!("--^^^------------------------------------------");
+        println!("");
+    }
+
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+macro_rules! dump_maybe {
+    ($args:expr, $input:expr) => {
+        #[cfg(feature="debug")]
+        crate::debug::inner::dump_maybe($args, $input);
+    }
+}
+pub(crate) use dump_maybe;
+
+macro_rules! dump_tokens {
+    ($name:expr, $ts:expr) => {
+        #[cfg(feature="debug")]
+        crate::debug::inner::dump_tokens($name, $ts);
+    }
+}
+pub(crate) use dump_tokens;
+
+macro_rules! dump_tokens2 {
+    ($name:expr, $ts:expr) => {
+        #[cfg(feature="debug")]
+        crate::debug::inner::dump_tokens2($name, $ts);
+    }
+}
+pub(crate) use dump_tokens2;
+
+macro_rules! dump_params {
+    ($name:expr, $params:expr) => {
+        #[cfg(feature="debug")]
+        crate::debug::inner::dump_params($name, $params);
+    }
+}
+pub(crate) use dump_params;