Download material property data as JSON

Return the property dataset as a JSON object mapping column name to value array.

Supports optional downsampling (max_points) and x-range filtering (x_col + x_min + x_max) for dynamic chart zoom resolution.

Example response::

{
    "c_e": [0.5, 1.0, 1.5, 2.0],
    "kappa": [0.42, 0.71, 0.89, 0.95],
    "diffusivity": [3.2e-10, 2.8e-10, 2.3e-10, 1.9e-10]
}