Web scraping to generate userstyles

### Is there an existing issue outlining your problem?

- [x] I have searched the existing issues and they do not solve my problem.

### Describe your issue.

Userstyles can be generated in combination with using Playwright to scrape the web pages, and LightningCSS to process and replace the colours.

There is a proof of concept at #2060.

Questions to answer:

- What are the maintenance costs of maintaining our own web scraper?
- What is the community sentiment on running a web scraper?
- Should the code be centralized so then it can be used for several userstyles? (e.g. Gmail, Crates.io)
- How should colour matching lists be defined in a maintainable way?

Start by reviewing the proof of concept in issue #2060 and trace how Playwright scraping and LightningCSS processing are used. Assess the maintenance cost, community implications, centralization across userstyles, and maintainability of colour-matching lists; done means documenting a decided direction for these questions.

Written by the indexing model from the issue text.