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/r0/CHANGELOG.md

@@ -0,0 +1,48 @@
+# Change Log
+
+All notable changes to this project will be documented in this file.
+This project adheres to [Semantic Versioning](http://semver.org/).
+
+## [Unreleased]
+
+## [v1.0.0] - 2020-03-03
+
+### Breaking Changes
+
+- Remove the init array APIs as they are not pulling their weight.
+- Bound `zero_bss` and `init_data` by a new `Word` trait.
+
+## [v0.2.2] - 2017-07-21
+
+### Changed
+
+- Optimized `zero_bss` and `init_data` for binary size. This change also results
+  in faster routines on non Cortex-M architectures.
+
+## [v0.2.1] - 2017-04-08
+
+### Added
+
+- `.init_array` / `.pre_init_array` support
+
+## [v0.2.0] - 2017-01-22
+
+### Changed
+
+- [breaking-change] The signature of the `zero_bss` and `init_data` functions;
+  the end `.bss`/`.data` pointer now must be `*mut T`. This makes it impossible
+  for people to bind a `static`, i.e. not `static mut`, variable to the end
+  of these sections, which could make the compiler, or other programmer, think
+  that such variable is allocated in the `.rodata` or the `.text` section.
+
+## v0.1.0 - 2016-10-03
+
+### Added
+
+- `init_data` and `zero_bss` functions.
+
+[Unreleased]: https://github.com/rust-embedded/r0/compare/v1.0.0...HEAD
+[v1.0.0]: https://github.com/rust-embedded/r0/compare/v0.2.2...v1.0.0
+[v0.2.2]: https://github.com/rust-embedded/r0/compare/v0.2.1...v0.2.2
+[v0.2.1]: https://github.com/rust-embedded/r0/compare/v0.2.0...v0.2.1
+[v0.2.0]: https://github.com/rust-embedded/r0/compare/v0.1.0...v0.2.0