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/metadata_blocks.rs

@@ -0,0 +1,181 @@
+// This file is auto-generated by the build script
+// Please, do not modify it manually
+
+use super::test_markdown_html;
+
+#[test]
+fn metadata_blocks_test_1() {
+    let original = r##"---
+title: example
+another_field: 0
+---
+"##;
+    let expected = r##""##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_2() {
+    let original = r##"---
+title: example
+another_field: 0
+"##;
+    let expected = r##"<hr>
+<p>title: example
+another_field: 0</p>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_3() {
+    let original = r##"---
+---
+"##;
+    let expected = r##"<hr>
+<hr>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_4() {
+    let original = r##"---
+
+title: example
+another_field: 0
+---
+"##;
+    let expected = r##"<hr>
+<h2>title: example
+another_field: 0</h2>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_5() {
+    let original = r##"My paragraph here.
+---
+title: example
+another_field: 0
+---
+"##;
+    let expected = r##"<h2>My paragraph here.</h2>
+<h2>title: example
+another_field: 0</h2>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_6() {
+    let original = r##"My paragraph here.
+
+---
+title: example
+another_field: 0
+---
+"##;
+    let expected = r##"<p>My paragraph here.</p>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_7() {
+    let original = r##"---    
+title: example
+another_field: 0
+---
+
+--- -
+title: example
+another_field: 0
+---
+"##;
+    let expected = r##"<hr>
+<h2>title: example
+another_field: 0</h2>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_8() {
+    let original = r##"---
+title: example
+another_field: 0
+---        
+
+---
+title: example
+another_field: 0
+---a
+"##;
+    let expected = r##"<hr>
+<p>title: example
+another_field: 0
+---a</p>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_9() {
+    let original = r##"---
+title: example
+another_field: 0
+...
+"##;
+    let expected = r##""##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_10() {
+    let original = r##"+++
+title: example
+another_field: 0
++++
+"##;
+    let expected = r##""##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_11() {
+    let original = r##"    ---
+    Things
+    ---
+"##;
+    let expected = r##"<pre><code>---
+Things
+---
+</code></pre>
+"##;
+
+    test_markdown_html(original, expected, false, true, false);
+}
+
+#[test]
+fn metadata_blocks_test_12() {
+    let original = r##"---
+- Item 1
+- Item 2
+---
+"##;
+    let expected = r##""##;
+
+    test_markdown_html(original, expected, false, true, false);
+}