- Change dark mode --color-well from #0a0a0a to #111111 for visible
contrast against #000000 background
- Add explicit text-fg class to balance display element to ensure
white text in dark mode
Add theme preference (light/dark/system) stored in extension state.
System mode follows prefers-color-scheme and listens for changes.
Dark mode inverts the monochrome palette (white-on-black).
Theme selector added to Display section in settings.
Closes#125
