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/embedded-storage-async/CHANGELOG.md

@@ -0,0 +1,27 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
+and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
+
+## [0.4.1] - 2023-11-28
+
+- Let `&mut` `NorFlash` implement `NorFlash`.
+- Reexport NOR flash errors from `embedded-storage`.
+- Use now stabilized `async_fn_in_trait` and `impl_trait_projections`.
+
+## [0.4.0] - 2022-12-01
+
+### Changes
+- Switch all traits to use [`async_fn_in_trait`](https://blog.rust-lang.org/inside-rust/2022/11/17/async-fn-in-trait-nightly.html) (AFIT). Requires `nightly-2022-11-22` or newer.
+- Remove `Async` prefix in trait names.
+
+## [0.3.0] - 2022-02-07
+
+Initial release to crates.io.
+
+[Unreleased]: https://github.com/rust-embedded-community/embedded-storage/compare/embedded-storage-async-v0.4.1...HEAD
+[0.4.1]: https://github.com/rust-embedded-community/embedded-storage/compare/embedded-storage-async-v0.4.0...embedded-storage-async-v0.4.1
+[0.4.0]: https://github.com/rust-embedded-community/embedded-storage/compare/embedded-storage-async-v0.3.0...embedded-storage-async-v0.4.0
+[0.3.0]: https://github.com/rust-embedded-community/embedded-storage/releases/tag/embedded-storage-async-v0.3.0