Marrow v1.3.1

Derived environment stats (dew point + altitude)

Two new zero-permission derived stats in EnvironmentHero:

Dew Point (°C) — computed from ambient temp + relative humidity via Magnus approximation. Shown when both sensors are available.

Altitude (m) — estimated from barometric pressure via ISA formula (±30–50 m accuracy). Shown when TYPE_PRESSURE is available.

No new permissions, no new sensors, no new StateFlows. Pure computed values from existing sensor readings.

10 unit tests. versionCode 101→102 / versionName 1.1.0→1.3.0.