fix: resolve 4 media embed bugs from testing

1. Video aspect ratio: remove container border/overflow-hidden, use
   preload="metadata" so browser knows dimensions before play
2. YouTube Error 153: remove sandbox attr (too restrictive), add full
   allow permissions (encrypted-media, accelerometer, gyroscope, etc.)
3. Google Images not displaying: detect image Content-Type from HTTP
   response in metadataFetcher, override classifier to create image
   embed for URLs that serve image/* content
4. Audio seeking broken: add HTTP Range request support in uploads
   route (Accept-Ranges, Content-Range, 206 Partial Content)

packages/server/src/utils/metadataFetcher.ts

@@ -22,6 +22,8 @@ export interface UrlMetadata {
   image: string | null;
   siteName: string | null;
   url: string;
+  /** Set when the URL itself is a direct media resource (image/video/audio) */
+  contentType?: string;
 }
 
 export async function fetchUrlMetadata(url: string): Promise<UrlMetadata | null> {
@@ -66,6 +68,13 @@ export async function fetchUrlMetadata(url: string): Promise<UrlMetadata | null>
       return null;
     }
 
+    // If the response is a direct media file (image/video/audio), return early
+    // with the content type — don't try to parse it as HTML
+    const responseContentType = response.headers.get('content-type') ?? '';
+    if (responseContentType.startsWith('image/') || responseContentType.startsWith('video/') || responseContentType.startsWith('audio/')) {
+      return { title: null, description: null, image: null, siteName: null, url, contentType: responseContentType };
+    }
+
     // Early exit if Content-Length > 512KB
     const contentLength = parseInt(response.headers.get('content-length') ?? '0', 10);
     if (contentLength > 512_000) {