feat: add media queue foundation

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/media/mediaQueue.ts

@@ -0,0 +1,59 @@
+import type {
+  MediaQueueItem,
+  MediaState,
+  ResolvedMediaSource,
+} from "./mediaTypes";
+
+export class MediaQueue {
+  private current: MediaQueueItem | null = null;
+  private readonly items: MediaQueueItem[] = [];
+
+  constructor(
+    private readonly createId = () => crypto.randomUUID(),
+    private readonly now = () => Date.now(),
+  ) {}
+
+  add(source: ResolvedMediaSource, requestedBy = "dashboard"): MediaQueueItem {
+    const item: MediaQueueItem = {
+      id: this.createId(),
+      mode: "music",
+      requestedBy,
+      addedAt: this.now(),
+      status: "queued",
+      ...source,
+    };
+    this.items.push(item);
+    return { ...item };
+  }
+
+  startNext(): MediaQueueItem | null {
+    if (this.current) return { ...this.current };
+    const next = this.items.shift();
+    if (!next) return null;
+    this.current = { ...next, status: "playing" };
+    return { ...this.current };
+  }
+
+  completeCurrent(): void {
+    this.current = null;
+  }
+
+  failCurrent(): void {
+    if (this.current) {
+      this.current = { ...this.current, status: "failed" };
+    }
+    this.current = null;
+  }
+
+  clear(): void {
+    this.current = null;
+    this.items.length = 0;
+  }
+
+  snapshot(): Pick<MediaState, "current" | "queue"> {
+    return {
+      current: this.current ? { ...this.current } : null,
+      queue: this.items.map((item) => ({ ...item })),
+    };
+  }
+}