feat(traffic): redesign admin traffic analytics

[attson]

Summary

• separate platform-only health data from user traffic analytics
• add user, category, direction, metric, and date-range filtering with timeline charts and drilldown
• add searchable user dropdown, responsive scrolling, and synchronized embedded web assets
• extend traffic and health APIs with daily buckets and relay status fields

Verification

• go test ./internal/relay
• desktop/frontend: 182 files, 2399 tests passed
• web: 29 files passed, 234 tests passed, 1 optional interop test skipped
• web contract: 16 tests passed
• desktop frontend production build passed
• scripts/build-web.sh passed with Node 20 and Go 1.23.12
• desktop and 390px mobile browser smoke checks passed