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.
