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/embassy-time/src/duration.rs

@@ -0,0 +1,219 @@
+use core::fmt;
+use core::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
+
+use super::{GCD_1K, GCD_1M, TICK_HZ};
+use crate::GCD_1G;
+
+#[derive(Debug, Default, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+/// Represents the difference between two [Instant](struct.Instant.html)s
+pub struct Duration {
+    pub(crate) ticks: u64,
+}
+
+impl Duration {
+    /// The smallest value that can be represented by the `Duration` type.
+    pub const MIN: Duration = Duration { ticks: u64::MIN };
+    /// The largest value that can be represented by the `Duration` type.
+    pub const MAX: Duration = Duration { ticks: u64::MAX };
+
+    /// Tick count of the `Duration`.
+    pub const fn as_ticks(&self) -> u64 {
+        self.ticks
+    }
+
+    /// Convert the `Duration` to seconds, rounding down.
+    pub const fn as_secs(&self) -> u64 {
+        self.ticks / TICK_HZ
+    }
+
+    /// Convert the `Duration` to milliseconds, rounding down.
+    pub const fn as_millis(&self) -> u64 {
+        self.ticks * (1000 / GCD_1K) / (TICK_HZ / GCD_1K)
+    }
+
+    /// Convert the `Duration` to microseconds, rounding down.
+    pub const fn as_micros(&self) -> u64 {
+        self.ticks * (1_000_000 / GCD_1M) / (TICK_HZ / GCD_1M)
+    }
+
+    /// Creates a duration from the specified number of clock ticks
+    pub const fn from_ticks(ticks: u64) -> Duration {
+        Duration { ticks }
+    }
+
+    /// Creates a duration from the specified number of seconds, rounding up.
+    pub const fn from_secs(secs: u64) -> Duration {
+        Duration { ticks: secs * TICK_HZ }
+    }
+
+    /// Creates a duration from the specified number of milliseconds, rounding up.
+    pub const fn from_millis(millis: u64) -> Duration {
+        Duration {
+            ticks: div_ceil(millis * (TICK_HZ / GCD_1K), 1000 / GCD_1K),
+        }
+    }
+
+    /// Creates a duration from the specified number of microseconds, rounding up.
+    /// NOTE: Delays this small may be inaccurate.
+    pub const fn from_micros(micros: u64) -> Duration {
+        Duration {
+            ticks: div_ceil(micros * (TICK_HZ / GCD_1M), 1_000_000 / GCD_1M),
+        }
+    }
+
+    /// Creates a duration from the specified number of nanoseconds, rounding up.
+    /// NOTE: Delays this small may be inaccurate.
+    pub const fn from_nanos(micros: u64) -> Duration {
+        Duration {
+            ticks: div_ceil(micros * (TICK_HZ / GCD_1G), 1_000_000_000 / GCD_1G),
+        }
+    }
+
+    /// Creates a duration from the specified number of seconds, rounding down.
+    pub const fn from_secs_floor(secs: u64) -> Duration {
+        Duration { ticks: secs * TICK_HZ }
+    }
+
+    /// Creates a duration from the specified number of milliseconds, rounding down.
+    pub const fn from_millis_floor(millis: u64) -> Duration {
+        Duration {
+            ticks: millis * (TICK_HZ / GCD_1K) / (1000 / GCD_1K),
+        }
+    }
+
+    /// Creates a duration from the specified number of microseconds, rounding down.
+    /// NOTE: Delays this small may be inaccurate.
+    pub const fn from_micros_floor(micros: u64) -> Duration {
+        Duration {
+            ticks: micros * (TICK_HZ / GCD_1M) / (1_000_000 / GCD_1M),
+        }
+    }
+
+    /// Creates a duration corresponding to the specified Hz.
+    /// NOTE: Giving this function a hz >= the TICK_HZ of your platform will clamp the Duration to 1
+    /// tick. Doing so will not deadlock, but will certainly not produce the desired output.
+    pub const fn from_hz(hz: u64) -> Duration {
+        let ticks = {
+            if hz >= TICK_HZ {
+                1
+            } else {
+                (TICK_HZ + hz / 2) / hz
+            }
+        };
+        Duration { ticks }
+    }
+
+    /// Adds one Duration to another, returning a new Duration or None in the event of an overflow.
+    pub fn checked_add(self, rhs: Duration) -> Option<Duration> {
+        self.ticks.checked_add(rhs.ticks).map(|ticks| Duration { ticks })
+    }
+
+    /// Subtracts one Duration to another, returning a new Duration or None in the event of an overflow.
+    pub fn checked_sub(self, rhs: Duration) -> Option<Duration> {
+        self.ticks.checked_sub(rhs.ticks).map(|ticks| Duration { ticks })
+    }
+
+    /// Multiplies one Duration by a scalar u32, returning a new Duration or None in the event of an overflow.
+    pub fn checked_mul(self, rhs: u32) -> Option<Duration> {
+        self.ticks.checked_mul(rhs as _).map(|ticks| Duration { ticks })
+    }
+
+    /// Divides one Duration a scalar u32, returning a new Duration or None in the event of an overflow.
+    pub fn checked_div(self, rhs: u32) -> Option<Duration> {
+        self.ticks.checked_div(rhs as _).map(|ticks| Duration { ticks })
+    }
+}
+
+impl Add for Duration {
+    type Output = Duration;
+
+    fn add(self, rhs: Duration) -> Duration {
+        self.checked_add(rhs).expect("overflow when adding durations")
+    }
+}
+
+impl AddAssign for Duration {
+    fn add_assign(&mut self, rhs: Duration) {
+        *self = *self + rhs;
+    }
+}
+
+impl Sub for Duration {
+    type Output = Duration;
+
+    fn sub(self, rhs: Duration) -> Duration {
+        self.checked_sub(rhs).expect("overflow when subtracting durations")
+    }
+}
+
+impl SubAssign for Duration {
+    fn sub_assign(&mut self, rhs: Duration) {
+        *self = *self - rhs;
+    }
+}
+
+impl Mul<u32> for Duration {
+    type Output = Duration;
+
+    fn mul(self, rhs: u32) -> Duration {
+        self.checked_mul(rhs)
+            .expect("overflow when multiplying duration by scalar")
+    }
+}
+
+impl Mul<Duration> for u32 {
+    type Output = Duration;
+
+    fn mul(self, rhs: Duration) -> Duration {
+        rhs * self
+    }
+}
+
+impl MulAssign<u32> for Duration {
+    fn mul_assign(&mut self, rhs: u32) {
+        *self = *self * rhs;
+    }
+}
+
+impl Div<u32> for Duration {
+    type Output = Duration;
+
+    fn div(self, rhs: u32) -> Duration {
+        self.checked_div(rhs)
+            .expect("divide by zero error when dividing duration by scalar")
+    }
+}
+
+impl DivAssign<u32> for Duration {
+    fn div_assign(&mut self, rhs: u32) {
+        *self = *self / rhs;
+    }
+}
+
+impl<'a> fmt::Display for Duration {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} ticks", self.ticks)
+    }
+}
+
+#[inline]
+const fn div_ceil(num: u64, den: u64) -> u64 {
+    (num + den - 1) / den
+}
+
+impl TryFrom<core::time::Duration> for Duration {
+    type Error = <u64 as TryFrom<u128>>::Error;
+
+    /// Converts using [`Duration::from_micros`]. Fails if value can not be represented as u64.
+    fn try_from(value: core::time::Duration) -> Result<Self, Self::Error> {
+        Ok(Self::from_micros(value.as_micros().try_into()?))
+    }
+}
+
+impl From<Duration> for core::time::Duration {
+    /// Converts using [`Duration::as_micros`].
+    fn from(value: Duration) -> Self {
+        core::time::Duration::from_micros(value.as_micros())
+    }
+}