Second step in the AdminTrafficUsage decomp. Move the 15 inline SVG
icons (Search/Chevron/Refresh/Download/Sort/Filter/Server/Calendar/X/
Status/Globe/Shield/ServerSmall) into a single barrel at
src/components/admin/trafficUsage/TrafficIcons.tsx. Pure SVG, no
behavioural change.
AdminTrafficUsage.tsx: 1734 → 1593 lines (-141).
