@spec absorbance_at(map(), float()) :: float()

Find the absorbance value at a specific wavelength.

If the spectrum has :corrected_absorbance, uses that. Otherwise uses :absorbance.

Extract metadata from a spectrum for this mode.

Returns a map of key-value pairs. Keys starting with underscore are considered private/internal (e.g., _baseline, _corrected_absorbance).

Generate SVG overlay elements from metadata.

The context map contains:

• :scale_x - function to convert wavelength to x pixel
• :scale_y - function to convert absorbance to y pixel
• :x_off, :y_off - chart offsets
• :width, :height - chart dimensions

Returns an SVG string to be inserted into the graph.

@spec safe_ratio(float(), float()) :: float() | nil

Safely compute a ratio, returning nil if denominator is zero or near-zero.