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-net-driver-channel/CHANGELOG.md

@@ -0,0 +1,30 @@
+# Changelog
+
+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
+
+## 0.3.2 - 2025-08-26
+
+## 0.3.1 - 2025-07-16
+
+- Update `embassy-sync` to v0.7.0
+
+## 0.3.0 - 2024-08-05
+
+- Add collapse_debuginfo to fmt.rs macros.
+- Update embassy-sync version
+
+## 0.2.0 - 2023-10-18
+
+- Update `embassy-net-driver` to v0.2
+- `Runner::new` now takes an `embassy_net_driver::HardwareAddress` parameter.
+- `Runner::set_ethernet_address` is now `set_hardware_address`.
+
+## 0.1.0 - 2023-06-29
+
+- First release