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,
 }