dark-pdf: Convert PDFs to dark mode while preserving the table of contents

Most 'dark mode' PDF solutions are either simple screen overlays that ignore document structure or clumsy converters that strip out metadata, leaving the user with a flat image of a page and a broken Table of Contents. dark-pdf takes a more surgical approach. By focusing on the preservation of the TOC, it ensures that the utility of the document remains intact even after the visual inversion, making it a genuine tool for long-form technical reading rather than just a visual gimmick. Technically, the tool is lean. It leverages a scale multiplier to balance output quality against file size and processing speed, which is a necessary inclusion given how PDF rendering can bloat files. The inclusion of a programmatic API suggests the author understands that while a CLI is great for one-off files, the real value lies in automating the conversion of entire libraries of documentation. However, the tool's current state is minimalist. With a small set of hardcoded themes and a dependency on JavaScript, it's a lightweight utility rather than a comprehensive PDF editor. The lack of advanced color-mapping—such as protecting specific image colors from inversion—means some documents may end up with 'inverted' photos that look unnatural. This is a solid win for developers and researchers who spend their nights scouring whitepapers and technical manuals. If you need a quick way to make a 200-page PDF readable at 2 AM without losing your navigation markers, this does exactly what it claims to do.