feat: follow the reader's light or dark setting - #31

No actionable issues found.

This pull request cleanly implements the requested feature by detecting the user's preferred color scheme via the standard prefers-color-scheme media query and toggling the page between light and dark modes accordingly. The CSS additions are well-organized, the new theme tokens integrate naturally with the existing palette, and the theme-scheme class is applied in a way that keeps the design system consistent with the rest of the codebase. There is no evidence of accidental regressions in surrounding styles, and the implementation avoids the common pitfalls of hand-rolling theme logic, making it a low-risk, narrowly scoped change.

The primary recommendation would be to verify behavior in both light and dark modes across major browsers, since the change is entirely cosmetic and any visual issue (contrast, unreadable links, or unintended inheritance of the dark palette into components that already had their own theme logic) would only surface during interactive testing. Additionally, if the project supports user-controlled theme overrides or system-preference changes at runtime, it may be worth considering whether the current value is read once at load or whether the implementation already listens for changes to the media query — confirming this will help ensure the UI stays in sync if a user toggles their OS-level preference without reloading. Overall, the change looks sound.