feat: resolve media music sources

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

src/media/mediaResolver.ts

@@ -0,0 +1,41 @@
+import { existsSync, statSync } from "node:fs";
+import path from "node:path";
+import { AppError } from "../errors";
+import type { ResolvedMediaSource } from "./mediaTypes";
+
+export async function resolveMediaSource(
+  input: string,
+): Promise<ResolvedMediaSource> {
+  const source = input.trim();
+  if (!source) {
+    throw new AppError("Media source is required", "MISSING_MEDIA_SOURCE", 400);
+  }
+
+  if (source.startsWith("http://") || source.startsWith("https://")) {
+    return {
+      source,
+      title: titleFromUrl(source),
+      kind: "url",
+    };
+  }
+
+  if (existsSync(source) && statSync(source).isFile()) {
+    return {
+      source,
+      title: path.basename(source),
+      kind: "local",
+    };
+  }
+
+  throw new AppError(
+    "Media source must be an HTTP(S) URL or existing local file",
+    "UNSUPPORTED_MEDIA_SOURCE",
+    400,
+  );
+}
+
+function titleFromUrl(source: string): string {
+  const url = new URL(source);
+  const filename = decodeURIComponent(url.pathname.split("/").pop() || "");
+  return filename || url.hostname;
+}