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/proc-macro2/tests/test_size.rs

@@ -0,0 +1,79 @@
+#![allow(unused_attributes)]
+
+extern crate proc_macro;
+
+use std::mem;
+
+#[cfg_attr(not(target_pointer_width = "64"), ignore = "only applicable to 64-bit")]
+#[cfg_attr(randomize_layout, ignore = "disabled due to randomized layout")]
+#[test]
+fn test_proc_macro_size() {
+    assert_eq!(mem::size_of::<proc_macro::Span>(), 4);
+    assert_eq!(mem::size_of::<Option<proc_macro::Span>>(), 4);
+    assert_eq!(mem::size_of::<proc_macro::Group>(), 20);
+    assert_eq!(mem::size_of::<proc_macro::Ident>(), 12);
+    assert_eq!(mem::size_of::<proc_macro::Punct>(), 8);
+    assert_eq!(mem::size_of::<proc_macro::Literal>(), 16);
+    assert_eq!(mem::size_of::<proc_macro::TokenStream>(), 4);
+}
+
+#[cfg_attr(not(target_pointer_width = "64"), ignore = "only applicable to 64-bit")]
+#[cfg_attr(randomize_layout, ignore = "disabled due to randomized layout")]
+#[cfg_attr(wrap_proc_macro, ignore = "wrapper mode")]
+#[cfg_attr(span_locations, ignore = "span locations are on")]
+#[test]
+fn test_proc_macro2_fallback_size_without_locations() {
+    assert_eq!(mem::size_of::<proc_macro2::Span>(), 0);
+    assert_eq!(mem::size_of::<Option<proc_macro2::Span>>(), 1);
+    assert_eq!(mem::size_of::<proc_macro2::Group>(), 16);
+    assert_eq!(mem::size_of::<proc_macro2::Ident>(), 24);
+    assert_eq!(mem::size_of::<proc_macro2::Punct>(), 8);
+    assert_eq!(mem::size_of::<proc_macro2::Literal>(), 24);
+    assert_eq!(mem::size_of::<proc_macro2::TokenStream>(), 8);
+}
+
+#[cfg_attr(not(target_pointer_width = "64"), ignore = "only applicable to 64-bit")]
+#[cfg_attr(randomize_layout, ignore = "disabled due to randomized layout")]
+#[cfg_attr(wrap_proc_macro, ignore = "wrapper mode")]
+#[cfg_attr(not(span_locations), ignore = "span locations are off")]
+#[test]
+fn test_proc_macro2_fallback_size_with_locations() {
+    assert_eq!(mem::size_of::<proc_macro2::Span>(), 8);
+    assert_eq!(mem::size_of::<Option<proc_macro2::Span>>(), 12);
+    assert_eq!(mem::size_of::<proc_macro2::Group>(), 24);
+    assert_eq!(mem::size_of::<proc_macro2::Ident>(), 32);
+    assert_eq!(mem::size_of::<proc_macro2::Punct>(), 16);
+    assert_eq!(mem::size_of::<proc_macro2::Literal>(), 32);
+    assert_eq!(mem::size_of::<proc_macro2::TokenStream>(), 8);
+}
+
+#[rustversion::attr(before(1.71), ignore = "requires Rust 1.71+")]
+#[cfg_attr(not(target_pointer_width = "64"), ignore = "only applicable to 64-bit")]
+#[cfg_attr(randomize_layout, ignore = "disabled due to randomized layout")]
+#[cfg_attr(not(wrap_proc_macro), ignore = "fallback mode")]
+#[cfg_attr(span_locations, ignore = "span locations are on")]
+#[test]
+fn test_proc_macro2_wrapper_size_without_locations() {
+    assert_eq!(mem::size_of::<proc_macro2::Span>(), 4);
+    assert_eq!(mem::size_of::<Option<proc_macro2::Span>>(), 8);
+    assert_eq!(mem::size_of::<proc_macro2::Group>(), 24);
+    assert_eq!(mem::size_of::<proc_macro2::Ident>(), 24);
+    assert_eq!(mem::size_of::<proc_macro2::Punct>(), 12);
+    assert_eq!(mem::size_of::<proc_macro2::Literal>(), 24);
+    assert_eq!(mem::size_of::<proc_macro2::TokenStream>(), 32);
+}
+
+#[cfg_attr(not(target_pointer_width = "64"), ignore = "only applicable to 64-bit")]
+#[cfg_attr(randomize_layout, ignore = "disabled due to randomized layout")]
+#[cfg_attr(not(wrap_proc_macro), ignore = "fallback mode")]
+#[cfg_attr(not(span_locations), ignore = "span locations are off")]
+#[test]
+fn test_proc_macro2_wrapper_size_with_locations() {
+    assert_eq!(mem::size_of::<proc_macro2::Span>(), 12);
+    assert_eq!(mem::size_of::<Option<proc_macro2::Span>>(), 12);
+    assert_eq!(mem::size_of::<proc_macro2::Group>(), 32);
+    assert_eq!(mem::size_of::<proc_macro2::Ident>(), 32);
+    assert_eq!(mem::size_of::<proc_macro2::Punct>(), 20);
+    assert_eq!(mem::size_of::<proc_macro2::Literal>(), 32);
+    assert_eq!(mem::size_of::<proc_macro2::TokenStream>(), 32);
+}