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/error.rs

@@ -0,0 +1,44 @@
+//! # Custom Errors
+//!
+//! A lot can be accomplished with the built-in error tools, like:
+//! - [`ContextError`]
+//! - [`Parser::context`]
+//! - [`cut_err`]
+//!
+//! *(see [tutorial][chapter_7])*
+//!
+//! Most other needs can likely be met by using a custom context type with [`ContextError`] instead
+//! of [`StrContext`].
+//! This will require implementing a custom renderer.
+//!
+//! ## `ParserError` Trait
+//!
+//! When needed, you can also create your own type that implements [`ParserError`].
+//!
+//! Optional traits include:
+//! - [`AddContext`]
+//! - [`FromExternalError`]
+//! - [`ErrorConvert`]
+//!
+//! There are multiple strategies for implementing support for [`AddContext`] and [`FromExternalError`]:
+//! - Make your error type generic over the context or external error
+//! - Require a trait for the context or external error and `Box` it
+//! - Make the context an enum like [`StrContext`]
+//! - Implement the trait multiple times, one for each concrete context or external error type,
+//!   allowing custom behavior per type
+//!
+//! Example:
+//!```rust
+#![doc = include_str!("../../examples/custom_error.rs")]
+//!```
+
+#![allow(unused_imports)]
+use crate::combinator::cut_err;
+use crate::error::ContextError;
+use crate::error::ErrorConvert;
+use crate::error::StrContext;
+use crate::Parser;
+use crate::_tutorial::chapter_7;
+use crate::error::AddContext;
+use crate::error::FromExternalError;
+use crate::error::ParserError;