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/use-moderation.ts

@@ -1,6 +1,12 @@
+import { useCallback, useEffect, useRef, useState } from "react";
 import useSWR from "swr";
 import { moderationApi } from "@/lib/api";
-import type { ModerationAction, ModerationStats } from "@/lib/types";
+import type {
+  ModerationAction,
+  ModerationStats,
+  ModerationTrends,
+} from "@/lib/types";
+import { useWebSocket } from "@/lib/ws/context";
 
 export function useModerationStats(initialData?: ModerationStats) {
   return useSWR<ModerationStats>(
@@ -33,3 +39,46 @@ export function useModerationActions(
     },
   );
 }
+
+/**
+ * Live moderation feed: merges the initial SWR list with actions pushed over
+ * the WebSocket in real time. Returns a capped, newest-first buffer.
+ * Read-only / public — no write actions.
+ */
+export function useLiveModeration(
+  initialData: ModerationAction[] = [],
+  cap = 50,
+) {
+  const { on: subscribe } = useWebSocket();
+  const [live, setLive] = useState<ModerationAction[]>(initialData);
+  const seen = useRef<Set<string>>(new Set(initialData.map((a) => a.id)));
+
+  useEffect(() => {
+    setLive(initialData);
+    seen.current = new Set(initialData.map((a) => a.id));
+  }, [initialData]);
+
+  const handle = useCallback(
+    (action: ModerationAction) => {
+      if (seen.current.has(action.id)) return;
+      seen.current.add(action.id);
+      setLive((prev) => [action, ...prev].slice(0, cap));
+    },
+    [cap],
+  );
+
+  useEffect(() => {
+    const unsub = subscribe("moderation_action", handle);
+    return unsub;
+  }, [subscribe, handle]);
+
+  return live;
+}
+
+export function useModerationTrends(days = 30, initialData?: ModerationTrends) {
+  return useSWR<ModerationTrends>(
+    ["moderation-trends", days],
+    () => moderationApi.getTrends(days),
+    { fallbackData: initialData },
+  );
+}