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/display-interface/CHANGELOG.md

@@ -0,0 +1,95 @@
+# 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]
+
+## Added
+
+- Updated to embedded-hal 1.0.0 and embedded-hal-async 1.0.0
+- New `AsyncWriteOnlyDataCommand` trait.
+- i2c, spi: `async/await` support.
+- parallel-gpio: Added `Generic16BitBus`
+- parallel-gpio: Added `PGPIO16BitInterface`
+- added `defmt-03` feature
+
+## Changed
+
+- **Breaking** raised MSRV to 1.75
+- spi: `SPIInterface` now wraps objects that implement the `SpiDeviceWrite` trait from embedded-hal 1.0.0
+- spi: `SPIInterface` now wraps objects that implement the `SpiDeviceWrite` trait from embedded-hal-async 1.0.0
+- parallel-gpio: Fixed bug with fallible pins
+- **Breaking** parallel-gpio: `GenericxBitBus::new` is now infallible
+
+## [v0.4.1] - 2021-05-10
+
+### Added
+
+- New `DisplayError` variant `RSError` to use with problems with the display's reset signal
+- New `DisplayError` variant `OutOfBoundsError` to use when writing to a non-existing pixel outside the display's bounds
+- parallel-gpio (0.5.0): New `OutputBus` trait
+- parallel-gpio (0.5.0): Added `Generic8BitBus`, an implementation of `OutputBus`
+
+### Changed
+
+- Return `DCError` instead of `BusWriteError` on errors (de-)asserting the DC signal in 8-bit GPIO interfaces
+- **Breaking** parallel-gpio (0.5.0): `PGPIO8BitInterface` now uses any 8-bit impementation of `OutputBus` instead of 8 individual pins
+
+## [v0.4.0] - 2020-05-25
+
+### Added
+
+- Support for 8bit and 16bit iterators as data format
+- Support for 16bit slice data format with target endian
+- Deconstructors for included display-interface implementations
+
+### Changed
+
+- Make enums non-exhaustive and added a DataFormatNotImplemented fallback error
+
+## [v0.3.0] - 2020-05-11
+
+### Added
+
+- 16 bit data width support for 8 bit parallel-gpio and SPI impls
+
+### Changed
+
+- Data width is provided via custom enum (breaking change)
+
+## [v0.2.1] - 2020-04-16
+
+### Added
+
+- Added prelude
+
+## [v0.2.0] - 2020-04-01
+
+### Changed
+
+- Made data width generic (breaking change)
+
+## [v0.1.1] - 2020-03-29
+
+### Fixed
+
+- Crate metadata
+
+### Removed
+
+- Examples requiring additional driver crates
+
+## 0.1.0 - 2020-03-29
+
+First version
+
+[Unreleased]: https://github.com/therealprof/display-interface/compare/v0.4.1...HEAD
+[v0.4.1]: https://github.com/therealprof/display-interface/compare/v0.4.0...v0.4.1
+[v0.4.0]: https://github.com/therealprof/display-interface/compare/v0.3.0...v0.4.0
+[v0.3.0]: https://github.com/therealprof/display-interface/compare/v0.2.1...v0.3.0
+[v0.2.1]: https://github.com/therealprof/display-interface/compare/v0.2.0...v0.2.1
+[v0.2.0]: https://github.com/therealprof/display-interface/compare/v0.1.1...v0.2.0
+[v0.1.1]: https://github.com/therealprof/display-interface/compare/v0.1.0...v0.1.1