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/lora-phy/src/mod_params.rs

@@ -0,0 +1,114 @@
+pub use lora_modulation::{Bandwidth, CodingRate, SpreadingFactor};
+
+/// Errors types reported during LoRa physical layer processing
+#[allow(clippy::upper_case_acronyms)]
+#[derive(Debug, defmt::Format, PartialEq)]
+#[allow(missing_docs)]
+pub enum RadioError {
+    SPI,
+    Reset,
+    RfSwitchRx,
+    RfSwitchTx,
+    Busy,
+    Irq,
+    DIO1,
+    InvalidConfiguration,
+    InvalidRadioMode,
+    OpError(u8),
+    InvalidBaseAddress(usize, usize),
+    PayloadSizeUnexpected(usize),
+    PayloadSizeMismatch(usize, usize),
+    UnavailableSpreadingFactor,
+    UnavailableBandwidth,
+    InvalidBandwidthForFrequency,
+    InvalidSF6ExplicitHeaderRequest,
+    InvalidOutputPowerForFrequency,
+    TransmitTimeout,
+    ReceiveTimeout,
+    DutyCycleUnsupported,
+    RngUnsupported,
+}
+
+/// Status for a received packet
+#[derive(Clone, Copy)]
+#[allow(missing_docs)]
+pub struct PacketStatus {
+    pub rssi: i16,
+    pub snr: i16,
+}
+
+/// The state of the radio
+#[derive(Clone, Copy, defmt::Format, PartialEq)]
+pub enum RadioMode {
+    /// Sleep mode
+    Sleep,
+    /// Standby mode
+    Standby,
+    /// Frequency synthesis mode
+    FrequencySynthesis,
+    /// Transmit (TX) mode
+    Transmit,
+    /// Receive (RX) mode
+    Receive(RxMode),
+    /// Channel activity detection (CAD) mode
+    ChannelActivityDetection,
+}
+
+impl From<RxMode> for RadioMode {
+    fn from(rx_mode: RxMode) -> Self {
+        RadioMode::Receive(rx_mode)
+    }
+}
+
+/// Listening mode for LoRaWAN packet detection/reception
+#[derive(Clone, Copy, defmt::Format, PartialEq)]
+pub enum RxMode {
+    /// Single shot Rx Mode to listen until packet preamble is detected or RxTimeout occurs.
+    /// The device will stay in RX Mode until a packet is received.
+    /// Preamble length as symbols is configured via following registers:
+    /// sx126x: uses `SetLoRaSymbNumTimeout(0 < n < 255)` + `SetStopRxTimerOnPreamble(1)`
+    /// sx127x: uses `RegSymbTimeout (4 < n < 1023)`
+    // TODO: Single mode with time-based timeout is available on sx126x, but not sx127x
+    Single(u16),
+    /// Continuous Rx mode to listen for incoming packets continuously
+    Continuous,
+    /// Receive in Duty Cycle mode (NB! Not supported on sx127x)
+    DutyCycle(DutyCycleParams),
+}
+
+/// Modulation parameters for a send and/or receive communication channel
+pub struct ModulationParams {
+    pub(crate) spreading_factor: SpreadingFactor,
+    pub(crate) bandwidth: Bandwidth,
+    pub(crate) coding_rate: CodingRate,
+    pub(crate) low_data_rate_optimize: u8,
+    pub(crate) frequency_in_hz: u32,
+}
+
+/// Packet parameters for a send or receive communication channel
+pub struct PacketParams {
+    pub(crate) preamble_length: u16,  // number of LoRa symbols in the preamble
+    pub(crate) implicit_header: bool, // if the header is explicit, it will be transmitted in the LoRa packet, but is not transmitted if the header is implicit (known fixed length)
+    pub(crate) payload_length: u8,
+    pub(crate) crc_on: bool,
+    pub(crate) iq_inverted: bool,
+}
+
+impl PacketParams {
+    pub(crate) fn set_payload_length(&mut self, payload_length: usize) -> Result<(), RadioError> {
+        if payload_length > 255 {
+            return Err(RadioError::PayloadSizeUnexpected(payload_length));
+        }
+        self.payload_length = payload_length as u8;
+        Ok(())
+    }
+}
+
+/// Receive duty cycle parameters
+#[derive(Clone, Copy, defmt::Format, PartialEq)]
+pub struct DutyCycleParams {
+    /// receive interval
+    pub rx_time: u32,
+    /// sleep interval
+    pub sleep_time: u32,
+}