refactor: move websocket and message queue to core/net

Reorganize project structure by relocating chat-websocket and message-queue modules from `src/integrations/` to `src/core/net/` to better reflect their networking purpose and improve code organization.

src/core/net/message-queue.ts

@@ -0,0 +1,74 @@
+/**
+ * 消息发送队列（限流）
+ *
+ * 原始 Dart: lib/core/net/message_queue.dart
+ *
+ * 业务行为：
+ *   - 入队消息按 `intervalMs` 间隔逐条发送（默认 1000ms）
+ *   - 消费者可声明每条消息是否成功消费；不成功则重新入队
+ *   - 队列可在任意时刻清空（dispose）
+ */
+export type MessageConsumer = (content: string) => boolean | Promise<boolean>;
+
+export class MessageQueue {
+  private queue: string[] = [];
+  private timer: ReturnType<typeof setTimeout> | null = null;
+  private disposed = false;
+  private consumer: MessageConsumer | null = null;
+
+  constructor(private readonly intervalMs = 1000) {}
+
+  /** 注册消费者（消费者必须能处理失败/重试）。 */
+  setConsumer(consumer: MessageConsumer): void {
+    this.consumer = consumer;
+  }
+
+  enqueue(content: string): void {
+    if (this.disposed) return;
+    this.queue.push(content);
+    if (!this.timer) this.scheduleNext();
+  }
+
+  private async attemptSend(next: string): Promise<void> {
+    if (!this.consumer) {
+      this.queue.unshift(next);
+      return;
+    }
+    let ok = false;
+    try {
+      ok = await this.consumer(next);
+    } catch (e) {
+      console.error("[MessageQueue] consumer error", e);
+      ok = false;
+    }
+    if (!ok) {
+      // 消费失败，放回队首等待下次
+      this.queue.unshift(next);
+    }
+  }
+
+  private scheduleNext(): void {
+    if (this.disposed) return;
+    const next = this.queue.shift();
+    if (next === undefined) {
+      this.timer = null;
+      return;
+    }
+    this.timer = setTimeout(() => {
+      void this.attemptSend(next).finally(() => this.scheduleNext());
+    }, this.intervalMs);
+  }
+
+  clear(): void {
+    this.queue = [];
+  }
+
+  dispose(): void {
+    this.disposed = true;
+    this.clear();
+    if (this.timer) {
+      clearTimeout(this.timer);
+      this.timer = null;
+    }
+  }
+}