How this works
The tropical zodiac starts at the equinox; the sidereal zodiac subtracts Lahiri ayanamsa. They are different systems, so both are labelled.
Approximate geocentric Sun/Moon calculations using the existing Meeus-based engine and a linear Lahiri ayanamsa. Near sign/Nakshatra boundaries, verify with a precise ephemeris. This is not a full Kundli.