feat(ogimage): render custom OG images for archive files

Add support for generating and rendering rich Open Graph (OG) image cards for archive files. When an archive file is shared, the handler now fetches or generates its listing metadata and renders a custom card displaying file/folder counts, uncompressed size, and a visual representation of the archive's contents.

backend/static/css/30-download.css

@@ -54,6 +54,20 @@
   margin: 0.45rem 0 0;
 }
 
+.preview-header > .button {
+  flex: 0 0 auto;
+  padding-inline: 1rem;
+  overflow: visible;
+}
+
+.preview-header > .button svg {
+  flex: 0 0 auto;
+}
+
+[data-theme="retro"] .preview-header > .button-primary:active {
+  padding-right: calc(1rem - 1px);
+}
+
 .preview-window {
   overflow: hidden;
   border: 1px solid color-mix(in srgb, var(--border) 78%, var(--primary));