feat: Pull Request - Accessibility Implementaion

@tjbck

I really like this product, but I was struggling to see some of the text. While you already have some good features, I’ve added some additional ones with the help of Claude. I would love to see these implemented. I’m happy for you to just take the code, make it your own, align it with how you do things, or allow me to open a PR.

Main features implemented

• Text contrast — new slider (0–100%) in Settings → Appearance that lifts all secondary text: muted labels, hints, timestamps, icons and input placeholders. Raises light-theme muted text from 3.19:1 to 7.81:1.
• Bold text — new toggle that raises the inherited body weight 400 → 500 and steps each explicit weight utility up one notch, so headings stay distinct.
• Border contrast ceiling raised — the existing control was capped at a 16% mix, topping out at 1.28:1 (an invisible border). Ceiling raised to 100%, making 3:1 reachable and a solid rule available at maximum.
• New "Readability" section — groups the above with UI Scale (moved up from the bottom of the panel), placed directly under Theme for discoverability.

https://github.com/aaronbolton/computer/pull/1

Start in Settings → Appearance and review the proposed implementation at the linked pull request. Confirm the Readability section, text contrast slider, bold-text toggle, border contrast ceiling, and UI Scale placement are implemented and accessible before considering the work done.