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/errors.rs

@@ -0,0 +1,140 @@
+use pulldown_cmark::{Options, Parser};
+
+fn parse(md: &str) {
+    let parser = Parser::new(md);
+
+    for _ in parser {}
+}
+
+fn parse_all_options(md: &str) {
+    let parser = Parser::new_ext(md, Options::all());
+
+    for _ in parser {}
+}
+
+#[test]
+fn test_lists_inside_code_spans() {
+    parse(
+        r"- `
+x
+**
+  *
+  `",
+    );
+}
+
+#[test]
+fn test_fuzzer_input_1() {
+    parse(">\n >>><N\n");
+}
+
+#[test]
+fn test_fuzzer_input_2() {
+    parse(" \u{b}\\\r- ");
+}
+
+#[test]
+fn test_fuzzer_input_3() {
+    parse_all_options("\n # #\r\u{1c} ");
+}
+
+#[test]
+fn test_fuzzer_input_4() {
+    parse_all_options("\u{0}{\tϐ}\n-");
+}
+
+#[test]
+fn test_fuzzer_input_5() {
+    parse_all_options(" \u{c}{}\n-\n");
+}
+
+#[test]
+fn test_fuzzer_input_6() {
+    parse("*\t[][\n\t<p]>\n\t[]");
+}
+
+#[test]
+fn test_fuzzer_input_7() {
+    parse_all_options("[][{]}\n-");
+}
+
+#[test]
+fn test_fuzzer_input_8() {
+    parse_all_options("a\n \u{c}{}\n-");
+}
+
+#[test]
+fn test_fuzzer_input_9() {
+    parse_all_options("a\n \u{c}{}\\\n-");
+}
+
+#[test]
+fn test_fuzzer_input_10() {
+    parse_all_options("[[    \t\n   \u{c}\u{c}\u{c}\u{c}\u{c}    {}\n-\r\u{e}\u{0}\u{0}{# }\n\u{b}\u{b}\u{b}\u{b}\u{b}\u{b}\u{b}\u{b}\u{b}\u{b}\u{0}\u{0}");
+}
+
+#[test]
+fn test_fuzzer_input_11() {
+    parse_all_options(
+        "[[\u{c}\u{c}   \t\n   \u{c}\u{c}\u{c}\u{c}\u{c}\u{c}\u{c}\u{c}\u{c}       {}\n-\r\u{e}",
+    );
+}
+
+#[test]
+fn test_fuzzer_input_12() {
+    parse_all_options("\u{c}-\n\u{c}\n-");
+}
+
+#[test]
+fn test_fuzzer_input_13() {
+    // Does not fail with Options::all():
+    Parser::new_ext(
+        ".\r> ^](\r\u{c}\r\0\0\r.\r[^\0\0\\\0\0\0^^^^^]",
+        Options::ENABLE_FOOTNOTES,
+    );
+}
+
+#[test]
+fn test_wrong_code_block() {
+    parse(
+        r##"```
+ * ```
+ "##,
+    );
+}
+
+#[test]
+fn test_unterminated_link() {
+    parse("[](\\");
+}
+
+#[test]
+fn test_unterminated_autolink() {
+    parse("<a");
+}
+
+#[test]
+fn test_infinite_loop() {
+    parse("[<!W\n\\\n");
+}
+
+#[test]
+fn test_html_tag() {
+    parse("<script\u{feff}");
+}
+
+// all of test_bad_slice_* were found in https://github.com/raphlinus/pulldown-cmark/issues/521
+#[test]
+fn test_bad_slice_a() {
+    parse("><a\n");
+}
+
+#[test]
+fn test_bad_slice_b() {
+    parse("><a a\n");
+}
+
+#[test]
+fn test_bad_slice_unicode() {
+    parse("><a a=\n毿>")
+}