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/basic-toml/tests/valid/table-array-many.json

@@ -0,0 +1,16 @@
+{
+    "people": [
+        {
+            "first_name": {"type": "string", "value": "Bruce"},
+            "last_name": {"type": "string", "value": "Springsteen"}
+        },
+        {
+            "first_name": {"type": "string", "value": "Eric"},
+            "last_name": {"type": "string", "value": "Clapton"}
+        },
+        {
+            "first_name": {"type": "string", "value": "Bob"},
+            "last_name": {"type": "string", "value": "Seger"}
+        }
+    ]
+}