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/chrono/tests/wasm.rs

@@ -0,0 +1,89 @@
+//! Run this test with:
+//! `env TZ="$(date +%z)" NOW="$(date +%s)" wasm-pack test --node -- --features wasmbind`
+//!
+//! The `TZ` and `NOW` variables are used to compare the results inside the WASM environment with
+//! the host system.
+//! The check will fail if the local timezone does not match one of the timezones defined below.
+
+#![cfg(all(
+    target_arch = "wasm32",
+    feature = "wasmbind",
+    feature = "clock",
+    not(any(target_os = "emscripten", target_os = "wasi"))
+))]
+
+use chrono::prelude::*;
+use wasm_bindgen_test::*;
+
+#[wasm_bindgen_test]
+fn now() {
+    let utc: DateTime<Utc> = Utc::now();
+    let local: DateTime<Local> = Local::now();
+
+    // Ensure time set by the test script is correct
+    let now = env!("NOW");
+    let actual = NaiveDateTime::parse_from_str(&now, "%s").unwrap().and_utc();
+    let diff = utc - actual;
+    assert!(
+        diff < chrono::TimeDelta::try_minutes(5).unwrap(),
+        "expected {} - {} == {} < 5m (env var: {})",
+        utc,
+        actual,
+        diff,
+        now,
+    );
+
+    let tz = env!("TZ");
+    eprintln!("testing with tz={}", tz);
+
+    // Ensure offset retrieved when getting local time is correct
+    let expected_offset = match tz {
+        "ACST-9:30" => FixedOffset::east_opt(19 * 30 * 60).unwrap(),
+        "Asia/Katmandu" => FixedOffset::east_opt(23 * 15 * 60).unwrap(), // No DST thankfully
+        "EDT" | "EST4" | "-0400" => FixedOffset::east_opt(-4 * 60 * 60).unwrap(),
+        "EST" | "-0500" => FixedOffset::east_opt(-5 * 60 * 60).unwrap(),
+        "UTC0" | "+0000" => FixedOffset::east_opt(0).unwrap(),
+        tz => panic!("unexpected TZ {}", tz),
+    };
+    assert_eq!(
+        &expected_offset,
+        local.offset(),
+        "expected: {:?} local: {:?}",
+        expected_offset,
+        local.offset(),
+    );
+}
+
+#[wasm_bindgen_test]
+fn from_is_exact() {
+    let now = js_sys::Date::new_0();
+
+    let dt = DateTime::<Utc>::from(now.clone());
+
+    assert_eq!(now.get_time() as i64, dt.timestamp_millis());
+}
+
+#[wasm_bindgen_test]
+fn local_from_local_datetime() {
+    let now = Local::now();
+    let ndt = now.naive_local();
+    let res = match Local.from_local_datetime(&ndt).single() {
+        Some(v) => v,
+        None => panic! {"Required for test!"},
+    };
+    assert_eq!(now, res);
+}
+
+#[wasm_bindgen_test]
+fn convert_all_parts_with_milliseconds() {
+    let time: DateTime<Utc> = "2020-12-01T03:01:55.974Z".parse().unwrap();
+    let js_date = js_sys::Date::from(time);
+
+    assert_eq!(js_date.get_utc_full_year(), 2020);
+    assert_eq!(js_date.get_utc_month(), 11); // months are numbered 0..=11
+    assert_eq!(js_date.get_utc_date(), 1);
+    assert_eq!(js_date.get_utc_hours(), 3);
+    assert_eq!(js_date.get_utc_minutes(), 1);
+    assert_eq!(js_date.get_utc_seconds(), 55);
+    assert_eq!(js_date.get_utc_milliseconds(), 974);
+}