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/strsim/tests/lib.rs

@@ -0,0 +1,71 @@
+extern crate strsim;
+
+use strsim::{
+    damerau_levenshtein, hamming, jaro, jaro_winkler, levenshtein, normalized_damerau_levenshtein,
+    normalized_levenshtein, osa_distance,
+};
+
+macro_rules! assert_delta {
+    ($x:expr, $y:expr) => {
+        assert_delta!($x, $y, 1e-5);
+    };
+    ($x:expr, $y:expr, $d:expr) => {
+        if ($x - $y).abs() > $d {
+            panic!(
+                "assertion failed: actual: `{}`, expected: `{}`: \
+                actual not within < {} of expected",
+                $x, $y, $d
+            );
+        }
+    };
+}
+
+#[test]
+fn hamming_works() {
+    match hamming("hamming", "hammers") {
+        Ok(distance) => assert_eq!(3, distance),
+        Err(why) => panic!("{:?}", why),
+    }
+}
+
+#[test]
+fn levenshtein_works() {
+    assert_eq!(3, levenshtein("kitten", "sitting"));
+}
+
+#[test]
+fn normalized_levenshtein_works() {
+    assert_delta!(0.57142, normalized_levenshtein("kitten", "sitting"));
+}
+
+#[test]
+fn osa_distance_works() {
+    assert_eq!(3, osa_distance("ac", "cba"));
+}
+
+#[test]
+fn damerau_levenshtein_works() {
+    assert_eq!(2, damerau_levenshtein("ac", "cba"));
+}
+
+#[test]
+fn normalized_damerau_levenshtein_works() {
+    assert_delta!(
+        0.27272,
+        normalized_damerau_levenshtein("levenshtein", "löwenbräu")
+    );
+}
+
+#[test]
+fn jaro_works() {
+    assert_delta!(
+        0.392,
+        jaro("Friedrich Nietzsche", "Jean-Paul Sartre"),
+        0.001
+    );
+}
+
+#[test]
+fn jaro_winkler_works() {
+    assert_delta!(0.866, jaro_winkler("cheeseburger", "cheese fries"), 0.001);
+}