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

Renders markdown to HTML. Returns the HTML string on both success and partial-error (Earmark may produce HTML even with warnings/errors).

@spec render_markdown_strict(String.t()) :: {:ok, String.t()} | {:error, list()}

Renders markdown to HTML, returning an ok/error tuple.

Returns {:ok, html} on success or {:error, errors} when Earmark cannot produce valid output.

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

Converts HTML to plain text for the text/plain part of emails.

Converts <br> tags to newlines, </p> to double newlines, and strips all remaining HTML tags.