@spec filename(String.t(), String.t()) :: String.t()

Builds a filename for an exported page. Format: monitorex{page}{timestamp}.{ext}

@spec sanitize_filename(String.t()) :: String.t()

Sanitizes a filename for safe filesystem use. Replaces non-alphanumeric characters (except . - _) with underscores.

@spec to_csv([map()], [atom()]) :: String.t()

Generates CSV string from a list of maps (rows) and column definitions.

Columns define both order and which keys to include. Handles commas, quotes, and newlines in cell values.

@spec to_json([map()], [atom()]) :: String.t()

Generates pretty-printed JSON from a list of maps or structs.

When fields is provided, only those keys are included (same as CSV export). Structs are converted to plain maps before encoding.