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-usb-driver/CHANGELOG.md

@@ -0,0 +1,13 @@
+# Changelog for embassy-usb-driver
+
+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).
+
+<!-- next-header -->
+## Unreleased - ReleaseDate
+
+## 0.1.1 - 2025-07-15
+
+- Add `embedded_io_async::Error` implementation for `EndpointError` ([#4176](https://github.com/embassy-rs/embassy/pull/4176))