feat(gmw): public features #2-#6 — live moderation feed, toxic topic trends, channel timeline, CSV export, activity heatmap

- Live Moderation Feed: gateway publishes discord:moderation:action (Redis) → backend WS emits moderation_action → public web shows realtime stream.
- Toxic Topic Trends: backend moderation.trends aggregates categories/severity/action_type (read-only) → SVG bar + donut.
- Channel Timeline: messages view gets Feed/Timeline toggle with date-grouped separators.
- CSV Export: client-side downloadCsv for moderation actions (no backend write scope).
- Activity Heatmap: backend messages.activity (per-hour volume by channel) → pure-SVG grid.

User reputation deliberately excluded — no such feature exists in the codebase.
All read-only / public-facing / fully automatic per project rules.

services/frontend/src/hooks/index.ts

@@ -30,10 +30,13 @@ export {
   useReview,
   useSemanticSearch,
   useTextChannels,
+  useMessageActivity,
 } from "./use-messages";
 export {
+  useLiveModeration,
   useModerationActions,
   useModerationStats,
+  useModerationTrends,
 } from "./use-moderation";
 export {
   useDeleteRecording,