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/embedded-can/src/lib.rs

@@ -0,0 +1,133 @@
+//! Controller Area Network (CAN) traits
+
+#![warn(missing_docs)]
+#![no_std]
+
+pub mod blocking;
+pub mod nb;
+
+mod id;
+
+pub use id::*;
+
+/// A CAN2.0 Frame
+pub trait Frame: Sized {
+    /// Creates a new frame.
+    ///
+    /// This will return `None` if the data slice is too long.
+    fn new(id: impl Into<Id>, data: &[u8]) -> Option<Self>;
+
+    /// Creates a new remote frame (RTR bit set).
+    ///
+    /// This will return `None` if the data length code (DLC) is not valid.
+    fn new_remote(id: impl Into<Id>, dlc: usize) -> Option<Self>;
+
+    /// Returns true if this frame is a extended frame.
+    fn is_extended(&self) -> bool;
+
+    /// Returns true if this frame is a standard frame.
+    fn is_standard(&self) -> bool {
+        !self.is_extended()
+    }
+
+    /// Returns true if this frame is a remote frame.
+    fn is_remote_frame(&self) -> bool;
+
+    /// Returns true if this frame is a data frame.
+    fn is_data_frame(&self) -> bool {
+        !self.is_remote_frame()
+    }
+
+    /// Returns the frame identifier.
+    fn id(&self) -> Id;
+
+    /// Returns the data length code (DLC) which is in the range 0..8.
+    ///
+    /// For data frames the DLC value always matches the length of the data.
+    /// Remote frames do not carry any data, yet the DLC can be greater than 0.
+    fn dlc(&self) -> usize;
+
+    /// Returns the frame data (0..8 bytes in length).
+    fn data(&self) -> &[u8];
+}
+
+/// CAN error
+pub trait Error: core::fmt::Debug {
+    /// Convert error to a generic CAN error kind
+    ///
+    /// By using this method, CAN errors freely defined by HAL implementations
+    /// can be converted to a set of generic serial errors upon which generic
+    /// code can act.
+    fn kind(&self) -> ErrorKind;
+}
+
+impl Error for core::convert::Infallible {
+    fn kind(&self) -> ErrorKind {
+        match *self {}
+    }
+}
+
+/// CAN error kind
+///
+/// This represents a common set of CAN operation errors. HAL implementations are
+/// free to define more specific or additional error types. However, by providing
+/// a mapping to these common CAN errors, generic code can still react to them.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[non_exhaustive]
+pub enum ErrorKind {
+    /// The peripheral receive buffer was overrun.
+    Overrun,
+
+    // MAC sublayer errors
+    /// A bit error is detected at that bit time when the bit value that is
+    /// monitored differs from the bit value sent.
+    Bit,
+
+    /// A stuff error is detected at the bit time of the sixth consecutive
+    /// equal bit level in a frame field that shall be coded by the method
+    /// of bit stuffing.
+    Stuff,
+
+    /// Calculated CRC sequence does not equal the received one.
+    Crc,
+
+    /// A form error shall be detected when a fixed-form bit field contains
+    /// one or more illegal bits.
+    Form,
+
+    /// An ACK  error shall be detected by a transmitter whenever it does not
+    /// monitor a dominant bit during the ACK slot.
+    Acknowledge,
+
+    /// A different error occurred. The original error may contain more information.
+    Other,
+}
+
+impl Error for ErrorKind {
+    fn kind(&self) -> ErrorKind {
+        *self
+    }
+}
+
+impl core::fmt::Display for ErrorKind {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::Overrun => write!(f, "The peripheral receive buffer was overrun"),
+            Self::Bit => write!(
+                f,
+                "Bit value that is monitored differs from the bit value sent"
+            ),
+            Self::Stuff => write!(f, "Sixth consecutive equal bits detected"),
+            Self::Crc => write!(f, "Calculated CRC sequence does not equal the received one"),
+            Self::Form => write!(
+                f,
+                "A fixed-form bit field contains one or more illegal bits"
+            ),
+            Self::Acknowledge => write!(f, "Transmitted frame was not acknowledged"),
+            Self::Other => write!(
+                f,
+                "A different error occurred. The original error may contain more information"
+            ),
+        }
+    }
+}