- General settings dialog: fill colors grouped by mode (light on/off, temp
cold/ok/hot, lqi weak/strong), each with its own opacity; lqi fill lerps
between the endpoints; stored in settings.fill_colors (defaults omitted);
space-card uses the same palette
- per-space show_lqi toggle (badges + room tooltip line), inherits the card's
show_signal when unset
- fillColorsOf/lerpColor/roomFillStyle helpers (+4 tests), backend schemas,
smoke_general_settings; TESTING.md updated in the same commit
