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/lib/api/messages.ts

@@ -1,6 +1,7 @@
 import { orpc } from "@/lib/orpc/client";
 import type {
   AttachmentRecord,
+  MessageActivityBucket,
   MessageRecord,
   SemanticSearchResult,
 } from "@/lib/types";
@@ -73,4 +74,10 @@ export const messagesApi = {
       results: SemanticSearchResult[];
       nextCursor: null;
     }>,
+
+  // Public, read-only activity heatmap data (per-hour volume by channel).
+  getActivity: (days = 30) =>
+    orpc.messages.activity({ days }) as unknown as Promise<
+      MessageActivityBucket[]
+    >,
 };

services/frontend/src/lib/api/moderation.ts

@@ -1,5 +1,9 @@
 import { orpc } from "@/lib/orpc/client";
-import type { ModerationStats, PaginatedModerationActions } from "@/lib/types";
+import type {
+  ModerationStats,
+  ModerationTrends,
+  PaginatedModerationActions,
+} from "@/lib/types";
 
 export const moderationApi = {
   getStats: () =>
@@ -17,4 +21,7 @@ export const moderationApi = {
       actionType,
       cursor,
     }) as unknown as Promise<PaginatedModerationActions>,
+
+  getTrends: (days = 30) =>
+    orpc.moderation.trends({ days }) as unknown as Promise<ModerationTrends>,
 };