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/src/offset/utc.rs

@@ -0,0 +1,159 @@
+// This is a part of Chrono.
+// See README.md and LICENSE.txt for details.
+
+//! The UTC (Coordinated Universal Time) time zone.
+
+use core::fmt;
+#[cfg(all(
+    feature = "now",
+    not(all(
+        target_arch = "wasm32",
+        feature = "wasmbind",
+        not(any(target_os = "emscripten", target_os = "wasi", target_os = "linux"))
+    ))
+))]
+use std::time::{SystemTime, UNIX_EPOCH};
+
+#[cfg(any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"))]
+use rkyv::{Archive, Deserialize, Serialize};
+
+use super::{FixedOffset, MappedLocalTime, Offset, TimeZone};
+use crate::naive::{NaiveDate, NaiveDateTime};
+#[cfg(feature = "now")]
+#[allow(deprecated)]
+use crate::{Date, DateTime};
+
+/// The UTC time zone. This is the most efficient time zone when you don't need the local time.
+/// It is also used as an offset (which is also a dummy type).
+///
+/// Using the [`TimeZone`](./trait.TimeZone.html) methods
+/// on the UTC struct is the preferred way to construct `DateTime<Utc>`
+/// instances.
+///
+/// # Example
+///
+/// ```
+/// use chrono::{DateTime, TimeZone, Utc};
+///
+/// let dt = DateTime::from_timestamp(61, 0).unwrap();
+///
+/// assert_eq!(Utc.timestamp_opt(61, 0).unwrap(), dt);
+/// assert_eq!(Utc.with_ymd_and_hms(1970, 1, 1, 0, 1, 1).unwrap(), dt);
+/// ```
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[cfg_attr(
+    any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"),
+    derive(Archive, Deserialize, Serialize),
+    archive(compare(PartialEq)),
+    archive_attr(derive(Clone, Copy, PartialEq, Eq, Debug, Hash))
+)]
+#[cfg_attr(feature = "rkyv-validation", archive(check_bytes))]
+#[cfg_attr(all(feature = "arbitrary", feature = "std"), derive(arbitrary::Arbitrary))]
+pub struct Utc;
+
+#[cfg(feature = "now")]
+impl Utc {
+    /// Returns a `Date` which corresponds to the current date.
+    #[deprecated(
+        since = "0.4.23",
+        note = "use `Utc::now()` instead, potentially with `.date_naive()`"
+    )]
+    #[allow(deprecated)]
+    #[must_use]
+    pub fn today() -> Date<Utc> {
+        Utc::now().date()
+    }
+
+    /// Returns a `DateTime<Utc>` which corresponds to the current date and time in UTC.
+    ///
+    /// See also the similar [`Local::now()`] which returns `DateTime<Local>`, i.e. the local date
+    /// and time including offset from UTC.
+    ///
+    /// [`Local::now()`]: crate::Local::now
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # #![allow(unused_variables)]
+    /// # use chrono::{FixedOffset, Utc};
+    /// // Current time in UTC
+    /// let now_utc = Utc::now();
+    ///
+    /// // Current date in UTC
+    /// let today_utc = now_utc.date_naive();
+    ///
+    /// // Current time in some timezone (let's use +05:00)
+    /// let offset = FixedOffset::east_opt(5 * 60 * 60).unwrap();
+    /// let now_with_offset = Utc::now().with_timezone(&offset);
+    /// ```
+    #[cfg(not(all(
+        target_arch = "wasm32",
+        feature = "wasmbind",
+        not(any(target_os = "emscripten", target_os = "wasi", target_os = "linux"))
+    )))]
+    #[must_use]
+    pub fn now() -> DateTime<Utc> {
+        let now =
+            SystemTime::now().duration_since(UNIX_EPOCH).expect("system time before Unix epoch");
+        DateTime::from_timestamp(now.as_secs() as i64, now.subsec_nanos()).unwrap()
+    }
+
+    /// Returns a `DateTime` which corresponds to the current date and time.
+    #[cfg(all(
+        target_arch = "wasm32",
+        feature = "wasmbind",
+        not(any(target_os = "emscripten", target_os = "wasi", target_os = "linux"))
+    ))]
+    #[must_use]
+    pub fn now() -> DateTime<Utc> {
+        let now = js_sys::Date::new_0();
+        DateTime::<Utc>::from(now)
+    }
+}
+
+impl TimeZone for Utc {
+    type Offset = Utc;
+
+    fn from_offset(_state: &Utc) -> Utc {
+        Utc
+    }
+
+    fn offset_from_local_date(&self, _local: &NaiveDate) -> MappedLocalTime<Utc> {
+        MappedLocalTime::Single(Utc)
+    }
+    fn offset_from_local_datetime(&self, _local: &NaiveDateTime) -> MappedLocalTime<Utc> {
+        MappedLocalTime::Single(Utc)
+    }
+
+    fn offset_from_utc_date(&self, _utc: &NaiveDate) -> Utc {
+        Utc
+    }
+    fn offset_from_utc_datetime(&self, _utc: &NaiveDateTime) -> Utc {
+        Utc
+    }
+}
+
+impl Offset for Utc {
+    fn fix(&self) -> FixedOffset {
+        FixedOffset::east_opt(0).unwrap()
+    }
+}
+
+impl fmt::Debug for Utc {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Z")
+    }
+}
+
+impl fmt::Display for Utc {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "UTC")
+    }
+}
+
+#[cfg(feature = "defmt")]
+impl defmt::Format for Utc {
+    fn format(&self, fmt: defmt::Formatter) {
+        defmt::write!(fmt, "Z");
+    }
+}