fix: correct drag coefficient label and units in ParabolicMotion

[TechGenius-Karan]

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🔍 Description

The drag input was labeled "Linear drag (1/s)" but the simulation calls
airResistance() with quadratic drag. This mislabels the physical quantity and gives
students the wrong units. Updated the label to "Quadratic drag (kg/m)" to match the
actual computation.

Closes #BUG-010 (if applicable)

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