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/nb/CHANGELOG.md

@@ -0,0 +1,46 @@
+# Change Log
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/)
+and this project adheres to [Semantic Versioning](http://semver.org/).
+
+## [Unreleased]
+
+## [v1.1.0] - 2023-03-07
+
+### Added
+
+- Add `defmt` as optional dependency and implement `defmt::Format` for `Error<E: defmt::Format>`, enabled by `defmt-0-3` unstable feature.
+
+## [v1.0.0] - 2020-07-07
+
+### Changed
+
+- [breaking-change] The `unstable` feature and its code has been removed.
+  This includes the macros `try_nb!` and `await!`.
+
+## [v0.1.2] - 2019-04-21
+
+### Added
+
+- `Error<E>` gained a `map` method that lets you transform the error in the
+  `Error::Other` variant into a different type.
+
+- `Error<E>` now implements the `From<E>` trait.
+
+## [v0.1.1] - 2018-01-10
+
+### Fixed
+
+- The `await!` macro now works when the expression `$e` mutably borrows `self`.
+
+## v0.1.0 - 2018-01-10
+
+Initial release
+
+[Unreleased]: https://github.com/rust-embedded/nb/compare/v1.1.0...HEAD
+[v1.1.0]: https://github.com/rust-embedded/nb/compare/v1.0.0...v1.1.0
+[v1.0.0]: https://github.com/rust-embedded/nb/compare/v0.1.2...v1.0.0
+[v0.1.2]: https://github.com/rust-embedded/nb/compare/v0.1.1...v0.1.2
+[v0.1.1]: https://github.com/rust-embedded/nb/compare/v0.1.0...v0.1.1