fix(boards): invert LilyGo T-Beam (classic) LED polarity via InvertedPin wrapper

The classic T-Beam's red LED on GPIO4 is wired active-low (anode to V+,
cathode to GPIO). Release v1.3.0 drove it as active-high, so the LED sat
lit at idle and dimmed briefly on TX/RX instead of flashing on activity.

Express the polarity where it physically lives — at the pin — via a new
generic InvertedPin<P> wrapper that swaps set_high/set_low. SimpleLed
stays polarity-agnostic and every other board's code path is
byte-for-byte unchanged from v1.3.0.

Empirically verified against hardware on both T-Beam boards: classic red
LED is now dark at idle and flashes on TX/RX; Supreme blue LED behaves
unchanged.

src/board/lilygo_tbeam.rs

@@ -13,7 +13,8 @@
 //!   LoRa ctl:  RESET=23, DIO0=26 (primary IRQ — SX127x has no BUSY)
 //!   OLED I²C:  SDA=21, SCL=22, SSD1306 @ 0x3C (shared with AXP192 @ 0x34)
 //!   UART host: TX=1, RX=3 via CP2102 bridge (USB 10c4:ea60)
-//!   LED:       GPIO4 (active HIGH — reuses MeshCore's P_LORA_TX_LED)
+//!   LED:       GPIO4 (active LOW — red LED under the OLED, wrapped in
+//!              InvertedPin so SimpleLed sees normal polarity)
 //!
 //! GPS / battery / IMU / PCF8563 RTC are populated on the board but unused
 //! by this firmware.
@@ -24,6 +25,7 @@ use esp_hal::i2c::master::{Config as I2cConfig, I2c};
 use super::esp32;
 use super::traits::{BoardParts, LoRaBoard};
 use crate::driver::axp;
+use crate::driver::inverted_pin::InvertedPin;
 use crate::driver::simple_led::SimpleLed;
 use crate::hal::esp32 as mcu;
 use crate::protocol::RadioChipId;
@@ -33,7 +35,7 @@ pub use super::esp32::{create_display, DisplayDriver, DisplayParts, RadioDriver,
 // ── Concrete peripheral types ───────────────────────────────────────
 
 pub type UartDriver = esp_hal::uart::Uart<'static, esp_hal::Async>;
-pub type LedDriver = SimpleLed<Output<'static>>;
+pub type LedDriver = SimpleLed<InvertedPin<Output<'static>>>;
 
 // ── Peripheral bundles ──────────────────────────────────────────────
 
@@ -122,9 +124,10 @@ impl LoRaBoard for Board {
             i2c: i2c_blocking.into_async(),
         });
 
-        // TX activity LED on GPIO4 (active HIGH).
-        let led_pin = Output::new(p.GPIO4, Level::Low, OutputConfig::default());
-        let led = SimpleLed(led_pin);
+        // TX activity LED on GPIO4 (active LOW — pin idles HIGH = LED off).
+        // InvertedPin flips set_high/set_low so SimpleLed stays polarity-agnostic.
+        let led_pin = Output::new(p.GPIO4, Level::High, OutputConfig::default());
+        let led = SimpleLed(InvertedPin(led_pin));
 
         BoardParts {
             radio,

src/driver/inverted_pin.rs

@@ -0,0 +1,30 @@
+//! Generic `OutputPin` wrapper that inverts logic levels.
+//!
+//! When a peripheral is wired active-low (LED anode to V+, cathode to GPIO;
+//! reset line idle-high, etc.) the physical polarity is a property of the
+//! board, not of the driver. Wrapping the pin in `InvertedPin` lets drivers
+//! keep "set_high = assert" semantics while the board file expresses the
+//! wiring reality at construction time.
+//!
+//! ```ignore
+//! let pin = Output::new(p.GPIO4, Level::High, OutputConfig::default()); // off
+//! let led = SimpleLed(InvertedPin(pin)); // driver sees normal polarity
+//! ```
+
+use embedded_hal::digital::{ErrorType, OutputPin};
+
+pub struct InvertedPin<P>(pub P);
+
+impl<P: ErrorType> ErrorType for InvertedPin<P> {
+    type Error = P::Error;
+}
+
+impl<P: OutputPin> OutputPin for InvertedPin<P> {
+    fn set_low(&mut self) -> Result<(), Self::Error> {
+        self.0.set_high()
+    }
+
+    fn set_high(&mut self) -> Result<(), Self::Error> {
+        self.0.set_low()
+    }
+}

src/driver/mod.rs

@@ -8,6 +8,9 @@ pub mod sh1106;
 #[cfg(any(feature = "lilygo_tbeam_supreme", feature = "lilygo_tbeam"))]
 pub mod axp;
 
+#[cfg(feature = "lilygo_tbeam")]
+pub mod inverted_pin;
+
 #[cfg(any(
     feature = "heltec_v3",
     feature = "heltec_v3_uart",