feat: Introduce new core components for conversation and speech management

- Added ConversationManager for managing conversation history with configurable limits.
- Implemented InputQueue for serial processing of input items.
- Created SpeechManager for handling text-to-speech generation and streaming.
- Developed StreamProcessor for processing LLM streams and forwarding events.
- Added TranscriptionManager for audio transcription using AI SDK.
- Introduced WebSocketManager for managing WebSocket connections and messaging.
- Updated VoiceAgent to support new architecture and improved socket handling.
- Refactored index files to export new core components.

src/core/InputQueue.ts

@@ -0,0 +1,71 @@
+/**
+ * A generic serial input queue that ensures only one processor runs at a time.
+ *
+ * @template T  The shape of each queued item (must include resolve/reject)
+ */
+export interface QueueItem<T = string> {
+  resolve: (v: T) => void;
+  reject: (e: unknown) => void;
+}
+
+export class InputQueue<T extends QueueItem<any>> {
+  private queue: T[] = [];
+  private processing = false;
+
+  /** Callback invoked for each item — must return a resolved value */
+  public processor: (item: T) => Promise<any> = async () => "";
+
+  /**
+   * Enqueue an item for serial processing.
+   */
+  enqueue(item: T): void {
+    this.queue.push(item);
+    this.drain();
+  }
+
+  /**
+   * Reject all pending items (used on disconnect/destroy).
+   */
+  rejectAll(reason: Error): void {
+    for (const item of this.queue) {
+      item.reject(reason);
+    }
+    this.queue = [];
+    this.processing = false;
+  }
+
+  /**
+   * Number of items waiting in the queue.
+   */
+  get length(): number {
+    return this.queue.length;
+  }
+
+  /**
+   * Whether the queue is currently processing an item.
+   */
+  get isProcessing(): boolean {
+    return this.processing;
+  }
+
+  // ── Private ──────────────────────────────────────────
+
+  private async drain(): Promise<void> {
+    if (this.processing) return;
+    this.processing = true;
+
+    try {
+      while (this.queue.length > 0) {
+        const item = this.queue.shift()!;
+        try {
+          const result = await this.processor(item);
+          item.resolve(result);
+        } catch (error) {
+          item.reject(error);
+        }
+      }
+    } finally {
+      this.processing = false;
+    }
+  }
+}