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/maybe-async-cfg/.versionrc

@@ -0,0 +1,14 @@
+{
+	"bumpFiles": [
+	{
+		"filename": "Cargo.toml",
+		"updater": ".standard-version/cargo-updater.js"
+	}
+  ],
+	"packageFiles": [
+	{
+		"filename": "Cargo.toml",
+		"updater": ".standard-version/cargo-updater.js"
+	}
+  ]
+}