feat(preview): add archive listing and browser support

Introduces the ability to browse and preview the contents of archive files directly within the web interface.

Changes include:
- Added a new API endpoint `GET /d/{boxID}/archive/{fileID}` to fetch archive listings.
- Implemented on-demand archive listing generation in the backend.
- Updated the frontend preview component to support rendering and navigating archive contents.

backend/static/css/30-download.css

@@ -271,6 +271,170 @@
   height: auto;
 }
 
+.archive-browser-preview {
+  width: 100%;
+  height: clamp(18rem, 64vh, 38rem);
+  overflow: auto;
+  background: color-mix(in srgb, var(--card) 86%, black 14%);
+  color: var(--foreground);
+}
+
+.archive-browser-header {
+  position: sticky;
+  top: 0;
+  z-index: 1;
+  display: flex;
+  flex-wrap: wrap;
+  align-items: baseline;
+  justify-content: space-between;
+  gap: 0.5rem 1rem;
+  padding: 0.9rem 1rem;
+  border-bottom: 1px solid var(--border);
+  background: color-mix(in srgb, var(--card) 92%, black 8%);
+}
+
+.archive-browser-header strong {
+  min-width: 0;
+  overflow-wrap: anywhere;
+  font-size: 0.98rem;
+}
+
+.archive-browser-header span {
+  color: var(--muted-foreground);
+  font-size: 0.82rem;
+}
+
+.archive-tree {
+  padding: 0.6rem 0.8rem 1rem;
+  font-family: Consolas, Monaco, "Andale Mono", "Ubuntu Mono", monospace;
+  font-size: 0.88rem;
+  line-height: 1.45;
+}
+
+.archive-node {
+  min-width: max-content;
+}
+
+.archive-node-row {
+  display: grid;
+  grid-template-columns: 1.25rem 1.45rem minmax(12rem, 1fr) auto;
+  align-items: center;
+  gap: 0.45rem;
+  min-height: 2.1rem;
+  padding: 0.18rem 0.45rem;
+  border-radius: 6px;
+  color: var(--foreground);
+}
+
+.archive-node-row:hover {
+  background: color-mix(in srgb, var(--accent) 12%, transparent);
+}
+
+.archive-folder > summary {
+  cursor: pointer;
+  list-style: none;
+}
+
+.archive-folder > summary::-webkit-details-marker {
+  display: none;
+}
+
+.archive-chevron,
+.archive-chevron-spacer,
+.archive-file-icon {
+  display: inline-grid;
+  place-items: center;
+  width: 1.25rem;
+  height: 1.25rem;
+}
+
+.archive-chevron {
+  color: var(--muted-foreground);
+  transition: transform 140ms ease, color 140ms ease;
+}
+
+.archive-folder[open] > summary .archive-chevron {
+  transform: rotate(90deg);
+  color: var(--accent);
+}
+
+.archive-chevron svg {
+  width: 1.18rem;
+  height: 1.18rem;
+}
+
+.archive-file-icon {
+  color: var(--muted-foreground);
+}
+
+.archive-file-icon svg,
+.archive-chevron svg {
+  fill: none;
+  stroke: currentColor;
+  stroke-width: 1.8;
+  stroke-linecap: round;
+  stroke-linejoin: round;
+}
+
+.archive-file-icon-folder {
+  color: var(--accent);
+}
+
+.archive-file-icon-folder svg {
+  fill: color-mix(in srgb, var(--accent) 18%, transparent);
+}
+
+.archive-file-icon-img {
+  color: #67e8f9;
+}
+
+.archive-file-icon-vid {
+  color: #f9a8d4;
+}
+
+.archive-file-icon-aud {
+  color: #86efac;
+}
+
+.archive-file-icon-code {
+  color: #c4b5fd;
+}
+
+.archive-file-icon-arc {
+  color: #fcd34d;
+}
+
+.archive-file-icon-txt {
+  color: #f8fafc;
+}
+
+.archive-node-name {
+  min-width: 0;
+  overflow-wrap: anywhere;
+}
+
+.archive-node-size {
+  color: var(--muted-foreground);
+  font-size: 0.78rem;
+}
+
+.archive-browser-empty {
+  margin: 0;
+  padding: 1rem;
+  color: var(--muted-foreground);
+}
+
+.archive-browser-legacy {
+  min-width: max-content;
+  margin: 0;
+  padding: 1rem;
+  color: var(--foreground);
+  font-family: Consolas, Monaco, "Andale Mono", "Ubuntu Mono", monospace;
+  font-size: 0.88rem;
+  line-height: 1.55;
+  white-space: pre;
+}
+
 .preview-placeholder {
   display: grid;
   place-items: center;
@@ -283,6 +447,7 @@
 .preview-placeholder[hidden],
 .default-preview[hidden],
 .native-preview[hidden],
+.archive-browser-preview[hidden],
 .large-preview-gate[hidden],
 .code-preview[hidden],
 .render-preview[hidden] {