refactor: rename rak_4631 to rak_wisblock_4631, add proper display names

Board naming now follows MeshCore conventions:
- rak_4631 → rak_wisblock_4631 (feature, file, Justfile, splash screen)
- Display splash shows human-readable names: "RAK WisBlock 4631",
  "Heltec v3", "Heltec v4"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/board/rak_wisblock_4631.rs

@@ -0,0 +1,114 @@
+use embassy_embedded_hal::shared_bus::asynch::spi::SpiDevice;
+use embassy_nrf::gpio::{AnyPin, Input, Level, Output, OutputDrive, Pull};
+use embassy_nrf::peripherals::USBD;
+use embassy_nrf::spim::{self, Spim};
+use embassy_nrf::twim::{self, Twim};
+use embassy_nrf::usb::Driver;
+use embassy_nrf::{bind_interrupts, Peripherals};
+use embassy_sync::blocking_mutex::raw::NoopRawMutex;
+use embassy_time::Delay;
+use static_cell::StaticCell;
+
+use lora_phy::iv::GenericSx126xInterfaceVariant;
+use lora_phy::sx126x::{self, Sx1262, Sx126x};
+
+bind_interrupts!(struct Irqs {
+    USBD => embassy_nrf::usb::InterruptHandler<USBD>;
+    SPIM3 => embassy_nrf::spim::InterruptHandler<embassy_nrf::peripherals::SPI3>;
+    SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0 => embassy_nrf::twim::InterruptHandler<embassy_nrf::peripherals::TWISPI0>;
+});
+
+// ── Concrete peripheral types ────────────────────────────────────────
+
+type SpiBus = Spim<'static, embassy_nrf::peripherals::SPI3>;
+type Nss = Output<'static>;
+type Iv = GenericSx126xInterfaceVariant<Output<'static>, Input<'static>>;
+type RadioSpiDevice = SpiDevice<'static, NoopRawMutex, SpiBus, Nss>;
+/// SX126x driver (pre-LoRa construction — LoRa::new is async).
+pub type RadioDriver = Sx126x<RadioSpiDevice, Iv, Sx1262>;
+
+/// USB driver for CDC-ACM.
+pub type UsbDriver = Driver<'static, USBD, &'static embassy_nrf::usb::vbus_detect::SoftwareVbusDetect>;
+
+/// I2C bus for an optional SSD1306 OLED.
+pub type DisplayI2c = Twim<'static, embassy_nrf::peripherals::TWISPI0>;
+
+// ── Peripheral bundles ───────────────────────────────────────────────
+
+pub struct RadioParts {
+    pub driver: RadioDriver,
+    pub delay: Delay,
+}
+
+pub struct UsbParts {
+    pub driver: UsbDriver,
+}
+
+pub struct DisplayParts {
+    pub i2c: DisplayI2c,
+}
+
+// ── Board init ───────────────────────────────────────────────────────
+
+pub struct Board {
+    p: Peripherals,
+}
+
+impl Board {
+    pub fn init() -> Self {
+        let p = embassy_nrf::init(Default::default());
+        Self { p }
+    }
+
+    pub fn into_parts(self) -> (RadioParts, UsbParts, Option<DisplayParts>) {
+        let p = self.p;
+
+        // ── SPI bus for SX1262 ───────────────────────────────────
+        let mut spi_cfg = spim::Config::default();
+        spi_cfg.frequency = spim::Frequency::M1;
+        let spi = Spim::new(p.SPI3, Irqs, p.P1_11, p.P1_13, p.P1_12, spi_cfg);
+
+        static SPI_BUS: StaticCell<embassy_sync::mutex::Mutex<NoopRawMutex, SpiBus>> =
+            StaticCell::new();
+        let spi_bus = SPI_BUS.init(embassy_sync::mutex::Mutex::new(spi));
+
+        let nss = Output::new(AnyPin::from(p.P1_10), Level::High, OutputDrive::Standard);
+        let spi_device = SpiDevice::new(spi_bus, nss);
+
+        // ── SX1262 control pins ──────────────────────────────────
+        let reset = Output::new(AnyPin::from(p.P1_06), Level::High, OutputDrive::Standard);
+        let dio1 = Input::new(AnyPin::from(p.P1_15), Pull::Down);
+        let busy = Input::new(AnyPin::from(p.P1_14), Pull::Down);
+
+        let iv = GenericSx126xInterfaceVariant::new(reset, dio1, busy, None, None).unwrap();
+
+        let sx_config = sx126x::Config {
+            chip: Sx1262,
+            tcxo_ctrl: Some(sx126x::TcxoCtrlVoltage::Ctrl1V7),
+            use_dcdc: true,
+            rx_boost: false,
+        };
+
+        let radio = RadioParts {
+            driver: Sx126x::new(spi_device, iv, sx_config),
+            delay: Delay,
+        };
+
+        // ── USB ──────────────────────────────────────────────────
+        static VBUS: StaticCell<embassy_nrf::usb::vbus_detect::SoftwareVbusDetect> =
+            StaticCell::new();
+        let vbus = VBUS.init(embassy_nrf::usb::vbus_detect::SoftwareVbusDetect::new(true, false));
+        let usb = UsbParts {
+            driver: Driver::new(p.USBD, Irqs, vbus),
+        };
+
+        // ── Display (optional RAK1921 SSD1306 OLED on I2C) ──────
+        // Always provide the I2C bus; display_task detects presence
+        // via SSD1306 init (fails gracefully if no display attached).
+        let i2c_cfg = twim::Config::default();
+        let i2c = Twim::new(p.TWISPI0, Irqs, p.P0_13, p.P0_14, i2c_cfg);
+        let display = Some(DisplayParts { i2c });
+
+        (radio, usb, display)
+    }
+}