Category picker: selected chips unreadable in dark mode (white text on bright green)

In dark mode, selected category chips in the org settings page use white text on a bright/fluorescent green background — very hard to read and visually jarring. The unselected chips look fine (outline style). Affects: org settings category picker, likely also event creation category picker and user interest picker (same CategoryPicker component). Fix: use a darker or muted green background with white text, or swap to dark text on green, specifically for dark mode. The selected state needs a dark-mode-aware color.