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/static_cell/CHANGELOG.md

@@ -0,0 +1,40 @@
+# 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).
+
+## 2.1.1 - 2025-06-22
+
+- Soundness fix: ConstStaticCell should only be Send/Sync if T: Send. (#19, #20)
+
+## 2.1.0 - 2024-04-26 - YANKED
+
+- Added `ConstStaticCell` (#14)
+
+## 2.0.0 - 2023-11-02
+
+- Do not enable feature `critical-section` in `portable-atomic`. In targets that need
+  atomic polyfilling, you now need to explicitly enable either of `critical-section` or
+  `unsafe-assume-single-core` in `portable-atomic`.
+
+## 1.3.0 - 2023-11-02
+
+- Switch from `atomic-polyfill` to `portable-atomic`. Note: to be backwards compatible
+  this crate is enabling the `critical-section` feature in `portable-atomic`. If your
+  chip is single-core, you might want to upgrade to `static-cell` v2.0 so you can enable
+  the feature `unsafe-assume-single-core` instead, which is slightly more efficient.
+
+## 1.2.0 - 2023-07-03
+
+- Add panic-free `try_init()`, `try_init_with()`, `try_uninit()`.
+
+## 1.1.0 - 2023-06-01
+
+- Add `uninit()`.
+- Add `make_static!` macro.
+
+## 1.0.0 - 2022-08-22
+
+- First release