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/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",