feat: Heltec V3 native USB, remove all dead_code suppressions

- heltec_v3 now uses USB OTG (requires hardware mod: solder R29/R3)
- heltec_v3_uart added as fallback for stock boards
- Removed every #[allow(dead_code)] — fixed root causes instead:
  - Comm types (UsbParts/UartParts) moved to individual board files
  - USB/UART init removed from hal (boards call esp-hal directly)
  - SH1106 driver gated on boards that use it
  - UART task sends DisplayCommand::Reset at startup (variant now used)
  - ErrorCode::CrcError removed (SX1262 drops bad-CRC silently)
- check/clippy now use --release (no more Xtensa dev-mode warnings)
- Updated README with hardware mod docs and board table

src/board/esp32s3.rs

@@ -1,7 +1,8 @@
 //! Shared types and peripheral wiring for ESP32-S3 boards.
 //!
 //! Delegates MCU-level init to `hal::esp32s3` and defines peripheral-level
-//! types (RadioDriver, Parts structs) used by ESP32-S3 board files.
+//! types (RadioDriver, display) used by ESP32-S3 board files.
+//! Each board defines its own comm types (UsbParts/UartParts) directly.
 
 use embassy_embedded_hal::shared_bus::asynch::spi::SpiDevice;
 use embassy_sync::blocking_mutex::raw::NoopRawMutex;
@@ -15,8 +16,7 @@ use crate::hal::esp32s3 as mcu;
 
 // ── Re-export MCU types ─────────────────────────────────────────────
 
-#[allow(unused_imports)] // Each board uses one of USB/UART, not both
-pub use mcu::{I2cBus as DisplayI2c, SpiBus, UartDriver, UsbOtgDriver as UsbDriver};
+pub use mcu::{I2cBus as DisplayI2c, SpiBus};
 
 // ── Concrete peripheral types ───────────────────────────────────────
 
@@ -32,16 +32,6 @@ pub struct RadioParts {
     pub delay: Delay,
 }
 
-#[allow(dead_code)] // Not used by heltec_v3_uart
-pub struct UsbParts {
-    pub driver: UsbDriver,
-}
-
-#[allow(dead_code)] // Only used by heltec_v3_uart
-pub struct UartParts {
-    pub driver: UartDriver,
-}
-
 pub struct DisplayParts {
     pub i2c: DisplayI2c,
 }

src/board/heltec_v3.rs

@@ -7,17 +7,22 @@
 //! For stock (unmodified) V3 boards, use the `heltec_v3_uart` feature instead.
 
 use esp_hal::gpio::{Level, Output, OutputConfig};
+use static_cell::StaticCell;
 
 use super::esp32s3;
 use super::traits::{BoardParts, LoRaBoard};
 use crate::hal::esp32s3 as mcu;
 
-#[allow(unused_imports)] // Re-exported for other modules (display, radio, host tasks)
 pub use super::esp32s3::{
-    create_display, DisplayDriver, DisplayI2c, DisplayParts, RadioDriver, RadioParts, UsbDriver,
-    UsbParts,
+    create_display, DisplayDriver, DisplayParts, RadioDriver, RadioParts,
 };
 
+pub type UsbDriver = esp_hal::otg_fs::asynch::Driver<'static>;
+
+pub struct UsbParts {
+    pub driver: UsbDriver,
+}
+
 pub struct Board {
     p: esp_hal::peripherals::Peripherals,
 }
@@ -53,9 +58,15 @@ impl LoRaBoard for Board {
         let radio = esp32s3::init_radio(spi_bus, p.GPIO8, p.GPIO12, p.GPIO14, p.GPIO13);
 
         // Note: switches internal USB PHY from Serial-JTAG to OTG.
-        // espflash --monitor will stop working after this point.
+        let usb_inst = esp_hal::otg_fs::Usb::new(p.USB0, p.GPIO20, p.GPIO19);
+        static EP_OUT_BUF: StaticCell<[u8; 1024]> = StaticCell::new();
+        let ep_out_buf = EP_OUT_BUF.init([0u8; 1024]);
         let host = UsbParts {
-            driver: mcu::init_usb(p.USB0, p.GPIO20, p.GPIO19),
+            driver: esp_hal::otg_fs::asynch::Driver::new(
+                usb_inst,
+                ep_out_buf,
+                esp_hal::otg_fs::asynch::Config::default(),
+            ),
         };
 
         // SSD1306 display reset: pulse GPIO21 low->high before I2C init

src/board/heltec_v3_uart.rs

@@ -12,12 +12,16 @@ use super::esp32s3;
 use super::traits::{BoardParts, LoRaBoard};
 use crate::hal::esp32s3 as mcu;
 
-#[allow(unused_imports)] // Re-exported for other modules (display, radio, host tasks)
 pub use super::esp32s3::{
-    create_display, DisplayDriver, DisplayI2c, DisplayParts, RadioDriver, RadioParts, UartDriver,
-    UartParts,
+    create_display, DisplayDriver, DisplayParts, RadioDriver, RadioParts,
 };
 
+pub type UartDriver = esp_hal::uart::Uart<'static, esp_hal::Async>;
+
+pub struct UartParts {
+    pub driver: UartDriver,
+}
+
 pub struct Board {
     p: esp_hal::peripherals::Peripherals,
 }
@@ -51,8 +55,14 @@ impl LoRaBoard for Board {
 
         let spi_bus = mcu::init_spi(p.SPI2, p.DMA_CH0, p.GPIO9, p.GPIO10, p.GPIO11);
         let radio = esp32s3::init_radio(spi_bus, p.GPIO8, p.GPIO12, p.GPIO14, p.GPIO13);
+
+        use esp_hal::uart::{Config as UartConfig, Uart};
         let host = UartParts {
-            driver: mcu::init_uart(p.UART0, p.GPIO43, p.GPIO44),
+            driver: Uart::new(p.UART0, UartConfig::default())
+                .expect("UART init")
+                .with_tx(p.GPIO43)
+                .with_rx(p.GPIO44)
+                .into_async(),
         };
 
         // SSD1306 display reset: pulse GPIO21 low->high before I2C init

src/board/heltec_v4.rs

@@ -1,15 +1,20 @@
 use esp_hal::gpio::{Level, Output, OutputConfig};
+use static_cell::StaticCell;
 
 use super::esp32s3;
 use super::traits::{BoardParts, LoRaBoard};
 use crate::hal::esp32s3 as mcu;
 
-#[allow(unused_imports)] // Re-exported for other modules (display, radio, host tasks)
 pub use super::esp32s3::{
-    create_display, DisplayDriver, DisplayI2c, DisplayParts, RadioDriver, RadioParts, UsbDriver,
-    UsbParts,
+    create_display, DisplayDriver, DisplayParts, RadioDriver, RadioParts,
 };
 
+pub type UsbDriver = esp_hal::otg_fs::asynch::Driver<'static>;
+
+pub struct UsbParts {
+    pub driver: UsbDriver,
+}
+
 pub struct Board {
     p: esp_hal::peripherals::Peripherals,
 }
@@ -45,8 +50,15 @@ impl LoRaBoard for Board {
         let radio = esp32s3::init_radio(spi_bus, p.GPIO8, p.GPIO12, p.GPIO14, p.GPIO13);
 
         // Note: switches internal USB PHY from Serial-JTAG to OTG.
+        let usb_inst = esp_hal::otg_fs::Usb::new(p.USB0, p.GPIO20, p.GPIO19);
+        static EP_OUT_BUF: StaticCell<[u8; 1024]> = StaticCell::new();
+        let ep_out_buf = EP_OUT_BUF.init([0u8; 1024]);
         let host = UsbParts {
-            driver: mcu::init_usb(p.USB0, p.GPIO20, p.GPIO19),
+            driver: esp_hal::otg_fs::asynch::Driver::new(
+                usb_inst,
+                ep_out_buf,
+                esp_hal::otg_fs::asynch::Config::default(),
+            ),
         };
 
         // SSD1315 display reset: pulse GPIO21 low->high before I2C init