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/memo-map/CHANGELOG.md

@@ -0,0 +1,33 @@
+# Changelog
+
+All notable changes to memo-map are documented here.
+
+## 0.3.3
+
+* Added `MemoMap::get_or_insert_owned` and `MemoMap::get_or_try_insert_owned`.
+
+## 0.3.2
+
+* Added `MemoMap::get_mut`, `MemoMap::iter_mut` and `MemoMap::values_mut`.
+
+## 0.3.1
+
+* Added `MemoMap::replace`.
+
+## 0.3.0
+
+* Box up individual values.  Previously this crate did not survive
+  resizes of the map in all circumstances.  This no longer requiers
+  `StableDeref` now at the cost of potential extra allocations.
+
+## 0.2.1
+
+* Fixed an incorrect statement in the readme.
+
+## 0.2.0
+
+* Added support for `remove` and `clear`.
+
+## 0.1.0
+
+* Initial release.