feat(backend): enhance social previews for single-file shares

Implements dynamic Open Graph (OG) metadata and image generation for
single-file shared boxes to improve social media previews.

Changes include:
- Added a new route `/d/{boxID}/f/{fileID}/og-image.jpg` for file-specific OG images.
- Updated `DownloadPage` to dynamically set the page title, description, and OG image properties when a box contains only one file.
- Restricted raw media inline serving for social bots to images and videos.
- Added helper functions to format file share descriptions and determine appropriate social image URLs and types.
- Integrated basic font rendering to support dynamic OG image generation.

backend/static/js/45-preview.js

@@ -110,19 +110,18 @@
   }
 
   function chooseDefaultMode(type, tabs) {
-    if (state.sizeBytes > LARGE_PREVIEW_BYTES) {
-      if (type.isAudio && hasMode(tabs, "browser-audio")) {
-        return "browser-audio";
-      }
-      return "default";
-    }
-
     if (type.isImage) {
       return "image";
     }
     if (type.isVideo) {
       return "video";
     }
+    if (state.sizeBytes > LARGE_PREVIEW_BYTES) {
+      if (type.isAudio && hasMode(tabs, "browser-audio")) {
+        return "browser-audio";
+      }
+      return "default";
+    }
     if (type.isAudio) {
       return "browser-audio";
     }