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/discord-gateway/src/modules/message-capture/moderationActionsDb.ts

@@ -4,8 +4,16 @@ import type * as schema from "../../shared/database/schema.js";
 import { moderationActionsTable } from "../../shared/database/schema.js";
 import { buildCursorCondition, pageResult } from "../../shared/index.js";
 import { createChildLogger, type Logger } from "../../shared/logger/index.js";
+import type { EventBroadcaster } from "../event-broadcaster/eventBroadcaster.js";
 import type { ModerationAction, PageResult } from "../message-capture/types.js";
 
+let _eventBroadcaster: EventBroadcaster | null = null;
+
+/** Inject the gateway's event broadcaster so actions can be published live. */
+export function setModerationEventBroadcaster(eb: EventBroadcaster): void {
+  _eventBroadcaster = eb;
+}
+
 // ─── ModerationActionsDb Class ──────────────────────────────────────────────
 
 export class ModerationActionsDb {
@@ -38,7 +46,16 @@ export class ModerationActionsDb {
         })
         .returning();
 
-      return rows[0] as ModerationAction;
+      const created = rows[0] as ModerationAction;
+
+      // Fire-and-forget live broadcast (backend WS → frontend feed).
+      if (_eventBroadcaster) {
+        _eventBroadcaster
+          .moderationAction(created as unknown as Record<string, unknown>)
+          .catch(() => {});
+      }
+
+      return created;
     } catch (error) {
       this.logger.error(
         {