fix: theme cascade system, peek as default, tag wrong-page fix
- Theme cascade: peek's variables.css prepended as base layer for all
non-peek themes, so themes only need to override colors
- Default theme changed from basic to peek
- Theme list sorted with peek first
- Shichijuni: brighten dark mode text (base03/base04) for readability,
remove font definitions (inherited from peek)
- Tags/entities: use getFocusedVisibleWindowId() instead of windows[0]
to tag the actually-focused page, not the oldest window