Add multi-session auth and changelog tracking

server/mediaService.ts

@@ -6,6 +6,16 @@ export type RemoteMediaSession = {
   userId: string;
   title: string;
   archiveStatus: "idle" | "queued" | "processing" | "completed" | "failed";
+  previewStatus?: "idle" | "processing" | "ready" | "failed";
+  previewSegments?: number;
+  markers?: Array<{
+    id: string;
+    type: string;
+    label: string;
+    timestampMs: number;
+    confidence?: number;
+    createdAt: string;
+  }>;
   playback: {
     webmUrl?: string;
     mp4Url?: string;