feat(push-gateway,msg): redis pubsub backplane for real-time notifications

M7: ADR-040 Redis Pub/Sub as state routing backplane

- push-gateway: remove Kafka consumer, add SSE endpoint

- SSE: subscribe to Redis user:{userId}:notify on connect

- msg: publish notifications to Redis Pub/Sub instead of HTTP push

- docker-compose: remove Kafka env from push-gateway

services/msg/src/channels/in-app.channel.ts

@@ -8,21 +8,24 @@ import type {
  * InAppChannel —— 站内信渠道。
  *
  * 站内信数据已在 NotificationService 中写入 MySQL + ES，
- * 此渠道仅负责触发 push-gateway 实时推送给在线用户（软失败）。
+ * 此渠道仅负责触发实时推送给在线用户（软失败）。
+ *
+ * M7 (ADR-040)：实时推送通过 Redis Pub/Sub backplane 发布到
+ * `user:{userId}:notify` 通道，realtime-gateway SSE 端点订阅并转发。
  *
  * 仲裁依据 02-architecture-design.md §2.4：
  * - in_app 总是发送，保证站内信可见
- * - 实时推送通过 push-gateway，不在线时用户下次拉取即可见
+ * - 实时推送通过 Redis Pub/Sub，不在线时用户下次拉取即可见
  */
-import { sendPush } from "../shared/push/push-gateway.client.js";
+import { publishToRedisPubSub } from "../shared/push/redis-publisher.js";
 import { logger } from "../shared/observability/logger.js";
 
 class InAppChannel implements NotificationChannelStrategy {
   readonly name = "in_app" as const;
 
   async send(ctx: ChannelSendContext): Promise<ChannelSendResult> {
-    // 站内信数据已落库，仅触发实时推送
-    const pushResult = await sendPush({
+    // 站内信数据已落库，仅触发实时推送（M7：Redis Pub/Sub backplane）
+    const pushResult = await publishToRedisPubSub({
       userId: ctx.userId,
       event: "notification.new",
       data: {
@@ -37,7 +40,7 @@ class InAppChannel implements NotificationChannelStrategy {
     if (!pushResult.sent) {
       logger.debug(
         { userId: ctx.userId, notificationId: ctx.notificationId },
-        "In-app push not delivered (user offline or gateway unavailable)",
+        "In-app real-time push not delivered (user offline or Redis unavailable)",
       );
     }
 

services/msg/src/channels/push.channel.ts

@@ -1,4 +1,4 @@
-import { sendPush } from "../shared/push/push-gateway.client.js";
+import { publishToRedisPubSub } from "../shared/push/redis-publisher.js";
 import type {
   ChannelSendContext,
   ChannelSendResult,
@@ -8,16 +8,16 @@ import type {
 /**
  * PushChannel —— 移动推送渠道。
  *
- * 通过 push-gateway HTTP /internal/push 推送。
- * 仲裁依据 M4：HTTP POST（豁免 gRPC）。
+ * M7 (ADR-040)：通过 Redis Pub/Sub backplane 发布到
+ * `user:{userId}:notify` 通道，realtime-gateway SSE 端点订阅并转发。
  *
- * 软失败：push-gateway 不可用或用户离线时返回 sent=false，不阻断。
+ * 软失败：Redis 不可用或用户离线时返回 sent=false，不阻断。
  */
 class PushChannel implements NotificationChannelStrategy {
   readonly name = "push" as const;
 
   async send(ctx: ChannelSendContext): Promise<ChannelSendResult> {
-    const result = await sendPush({
+    const result = await publishToRedisPubSub({
       userId: ctx.userId,
       event: "notification.push",
       data: {