feat(13-07): implement sequential cloud upload queue with typed pause/resume

- StorageBrowser: add conflict dialog (D-03) and error dialog (D-04) for paused queue states
- StorageBrowser: add upload-queue-resolve emit for Keep both / Replace / Skip / Retry / Cancel all actions
- StorageBrowser: add upload-queue-list with upload-queue-item rows for remaining queued items
- StorageBrowser: suppress UploadProgress in cloud mode (replaced by queue dialogs)
- CloudFolderView: replace placeholder onFilesSelected with sequential queue runner
- CloudFolderView: handle upload-queue-resolve events for all conflict/error resolution actions
- api/cloud.js: add conflictAction param to uploadCloudFile for keep_both/replace paths
- api/cloud.js: add downloadCloudFile authorized fallback helper
- CloudFolderView.test.js: fix CapturingStub missing name, add uploadCloudFile mock
- All 34 queue and thin-view tests pass (StorageBrowser.cloud-queue + CloudFolderView)

frontend/src/api/cloud.js

@@ -131,8 +131,12 @@ export function testCloudConnection(connectionId) {
  * D-02: Provider credentials and raw provider URLs are never exposed.
  * Returns {kind: 'open', url: '<authorized-docuvault-url>'}.
  * The caller must navigate to the returned URL — never window.open to a provider URL.
+ *
+ * @param {string} connectionId - Connection UUID
+ * @param {string} itemId - Provider item ID (opaque reference)
+ * @param {object} [fileContext] - Optional file metadata context (name, contentType) for display
  */
-export function openCloudFile(connectionId, itemId) {
+export function openCloudFile(connectionId, itemId, fileContext) {
   return request(`/api/cloud/connections/${connectionId}/items/${encodeURIComponent(itemId)}/open`)
 }
 
@@ -222,14 +226,32 @@ export function deleteCloudItem(connectionId, itemId) {
  * @param {string} parentRef - Parent folder provider_item_id
  * @param {string} filename - Target filename
  * @param {File|Blob} file - File bytes
+ * @param {'keep_both'|'replace'|undefined} conflictAction - Optional conflict resolution action
  */
-export function uploadCloudFile(connectionId, parentRef, filename, file) {
+export function uploadCloudFile(connectionId, parentRef, filename, file, conflictAction) {
   const formData = new FormData()
   formData.append('file', file, filename)
   formData.append('parent_ref', parentRef ?? '')
   formData.append('filename', filename)
+  if (conflictAction) formData.append('conflict_action', conflictAction)
   return request(`/api/cloud/connections/${connectionId}/items/upload`, {
     method: 'POST',
     body: formData,
   })
 }
+
+/**
+ * Download a cloud file through the DocuVault authorized download endpoint.
+ *
+ * D-02: No raw provider URL or credential is exposed.
+ * D-18: Used as a fallback for unsupported preview formats (Office, Workspace).
+ *       The authorized endpoint serves bytes through DocuVault's own proxy.
+ *
+ * Returns {kind: 'download', url: '<docuvault-relative-url>'}.
+ */
+export function downloadCloudFile(connectionId, itemId) {
+  return request(
+    `/api/cloud/connections/${connectionId}/items/${encodeURIComponent(itemId)}/download`,
+    { method: 'GET' },
+  )
+}