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/winnow/src/_topic/performance.rs

@@ -0,0 +1,55 @@
+//! # Performance
+//!
+//! ## Runtime Performance
+//!
+//! See also the general Rust [Performance Book](https://nnethercote.github.io/perf-book/)
+//!
+//! Tips
+//! - Try `cargo add winnow -F simd`. For some it offers significant performance improvements
+//! - When enough cases of an [`alt`] have unique prefixes, prefer [`dispatch`]
+//! - When parsing text, try to parse as bytes (`u8`) rather than `char`s ([`BStr`] can make
+//!   debugging easier)
+//! - Find simplified subsets of the grammar to parse, falling back to the full grammar when it
+//!   doesn't work. For example, when parsing json strings, parse them without support for escapes,
+//!   falling back to escape support if it fails.
+//! - Watch for large return types. A surprising place these can show up is when chaining parsers
+//!   with a tuple.
+//!
+//! ## Build-time Performance
+//!
+//! Returning complex types as `impl Trait` can negatively impact build times. This can hit in
+//! surprising cases like:
+//! ```rust
+//! # use winnow::prelude::*;
+//! fn foo<I, O, E>() -> impl Parser<I, O, E>
+//! # where
+//! #    I: winnow::stream::Stream<Token=O>,
+//! #    I: winnow::stream::StreamIsPartial,
+//! #    E: winnow::error::ParserError<I>,
+//! {
+//!     // ...some chained combinators...
+//! # winnow::token::any
+//! }
+//! ```
+//!
+//! Instead, wrap the combinators in a closure to simplify the type:
+//! ```rust
+//! # use winnow::prelude::*;
+//! fn foo<I, O, E>() -> impl Parser<I, O, E>
+//! # where
+//! #    I: winnow::stream::Stream<Token=O>,
+//! #    I: winnow::stream::StreamIsPartial,
+//! #    E: winnow::error::ParserError<I>,
+//! {
+//!     move |input: &mut I| {
+//!         // ...some chained combinators...
+//! # winnow::token::any
+//!             .parse_next(input)
+//!     }
+//! }
+//! ```
+
+#![allow(unused_imports)]
+use crate::combinator::alt;
+use crate::combinator::dispatch;
+use crate::stream::BStr;