feat(server): track upload status via manifest and /status API

- Persist per-box file metadata in a .warpbox.json manifest, including IDs and status fields (pending/uploading/complete/failed)
- Add GET /box/:id/status to return current file states for clients polling upload progress
- Update upload handling to mark failures and completion in the manifest and decorate responses
- Add CSS states for loading/failed files and disable interactions for unavailable itemsfeat(server): track upload status via manifest and /status API

- Persist per-box file metadata in a .warpbox.json manifest, including IDs and status fields (pending/uploading/complete/failed)
- Add GET /box/:id/status to return current file states for clients polling upload progress
- Update upload handling to mark failures and completion in the manifest and decorate responses
- Add CSS states for loading/failed files and disable interactions for unavailable items

static/css/box.css

@@ -74,6 +74,28 @@
     text-decoration: none;
 }
 
+.box-file.is-loading,
+.box-file.is-failed {
+    color: #666666;
+    filter: grayscale(1);
+}
+
+.box-file.is-loading {
+    animation: box-loading-pulse 900ms steps(2, end) infinite;
+}
+
+.box-file.is-failed {
+    opacity: 0.58;
+}
+
+.box-file.is-failed .box-file-name::after {
+    content: " (failed)";
+}
+
+.box-file[aria-disabled="true"] {
+    cursor: default;
+}
+
 .box-file:hover,
 .box-file:focus-visible {
     color: #ffffff;
@@ -99,6 +121,16 @@
     white-space: nowrap;
 }
 
+@keyframes box-loading-pulse {
+    0% {
+        opacity: 0.48;
+    }
+
+    100% {
+        opacity: 0.82;
+    }
+}
+
 .box-file-name {
     font-size: 13px;
     line-height: 13px;