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/pulldown-cmark/tests/suite/mod.rs

@@ -0,0 +1,19 @@
+// This file is auto-generated by the build script
+// Please, do not modify it manually
+
+pub use super::test_markdown_html;
+
+mod blockquotes_tags;
+mod footnotes;
+mod gfm_strikethrough;
+mod gfm_table;
+mod gfm_tasklist;
+mod heading_attrs;
+mod math;
+mod metadata_blocks;
+mod old_footnotes;
+mod regression;
+mod smart_punct;
+mod spec;
+mod strikethrough;
+mod table;