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/enumset_derive/src/lib.rs

@@ -0,0 +1,26 @@
+#![recursion_limit = "256"]
+
+mod const_eval;
+mod gen;
+mod plan;
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use std::fmt::Display;
+use syn::{parse_macro_input, DeriveInput};
+
+/// Helper function for emitting compile errors.
+fn error<T>(span: proc_macro2::Span, message: impl Display) -> syn::Result<T> {
+    Err(syn::Error::new(span, message))
+}
+
+#[proc_macro_derive(EnumSetType, attributes(enumset))]
+pub fn derive_enum_set_type(input: TokenStream) -> TokenStream {
+    let input: DeriveInput = parse_macro_input!(input);
+    derive_enum_set_type_0(input).unwrap_or_else(|e| e.to_compile_error().into())
+}
+fn derive_enum_set_type_0(input: DeriveInput) -> syn::Result<TokenStream> {
+    let plan = plan::plan_for_enum(input)?;
+    Ok(gen::generate_code(plan).into())
+}