feat: implement user session management with Redis and add game token verification

app/gateway-api/src/auth/flushPublisher.ts

@@ -0,0 +1,28 @@
+export interface GatewayUserFlushEvent {
+    userId: string;
+    flushedAt: string;
+    reason?: string;
+}
+
+export interface GatewayFlushPublisher {
+    publishUserFlush(userId: string, reason?: string): Promise<void>;
+}
+
+export class RedisGatewayFlushPublisher implements GatewayFlushPublisher {
+    private readonly channel: string;
+    private readonly client: { publish: (channel: string, message: string) => Promise<number> };
+
+    constructor(client: { publish: (channel: string, message: string) => Promise<number> }, channel: string) {
+        this.client = client;
+        this.channel = channel;
+    }
+
+    async publishUserFlush(userId: string, reason?: string): Promise<void> {
+        const payload: GatewayUserFlushEvent = {
+            userId,
+            flushedAt: new Date().toISOString(),
+            reason,
+        };
+        await this.client.publish(this.channel, JSON.stringify(payload));
+    }
+}