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/embassy-embedded-hal/CHANGELOG.md

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+# Changelog for embassy-embedded-hal
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## Unreleased
+
+## 0.2.0 - 2024-08-05
+
+- Add Clone derive to flash Partition in embassy-embedded-hal
+- Add support for all word sizes to async shared spi
+- Add Copy and 'static constraint to Word type in SPI structs
+- Improve flexibility by introducing SPI word size as a generic parameter
+- Allow changing Spi/I2cDeviceWithConfig's config at runtime
+- Impl `MultiwriteNorFlash` for `BlockingAsync`
+
+## 0.1.0 - 2024-01-10
+
+- First release