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/mod.rs

@@ -0,0 +1,43 @@
+//! # Special Topics
+//!
+//! These are short recipes for accomplishing common tasks.
+//!
+//! - [Why `winnow`?][why]
+//! - [For `nom` users][nom]
+//! - Formats:
+//!   - [Elements of Programming Languages][language]
+//!   - [Arithmetic][arithmetic]
+//!   - [s-expression][s_expression]
+//!   - [json]
+//!   - [INI][ini]
+//!   - [HTTP][http]
+//! - Special Topics:
+//!   - [Implementing `FromStr`][fromstr]
+//!   - [Performance][performance]
+//!   - [Parsing Partial Input][partial]
+//!   - [Lexing and Parsing][lexing]
+//!   - [Custom stream or token][stream]
+//!   - [Custom errors][error]
+//!   - [Debugging][crate::_tutorial::chapter_8]
+//!
+//! See also parsers written with `winnow`:
+//!
+//! - [`toml_edit`](https://crates.io/crates/toml_edit)
+//! - [`hcl-edit`](https://crates.io/crates/hcl-edit)
+#![allow(clippy::std_instead_of_core)]
+#![allow(clippy::test_attr_in_doctest)]
+
+pub mod arithmetic;
+pub mod error;
+pub mod fromstr;
+pub mod http;
+pub mod ini;
+pub mod json;
+pub mod language;
+pub mod lexing;
+pub mod nom;
+pub mod partial;
+pub mod performance;
+pub mod s_expression;
+pub mod stream;
+pub mod why;