feat(12-03): connection-ID routing, rename, session folder memory, thin views

- Route /cloud/:connectionId/:folderId replaces /cloud/:provider/:folderId
- api/cloud.js: getCloudFoldersByConnectionId + renameCloudConnection
- cloudConnections store: rename, selectConnection, setBrowseState, defaultDisplayName, session storage helpers
- CloudStorageView: thin — passes connectionRoots to StorageBrowser
- CloudFolderView: thin — uses connectionId param, never provider slug
- SettingsCloudTab: inline rename input for each active connection
- 27 tests pass: store, view, settings

frontend/src/api/cloud.js

@@ -29,10 +29,26 @@ export function updateDefaultStorage(backend) {
   return jsonRequest('/api/users/me/default-storage', 'PATCH', { backend })
 }
 
+/**
+ * Browse a cloud folder by connection UUID and folder path.
+ * connectionId is always a UUID; folderId is a path string (default 'root').
+ */
+export function getCloudFoldersByConnectionId(connectionId, folderId) {
+  return request(`/api/cloud/connections/${connectionId}/folders/${folderId}`)
+}
+
+/** @deprecated Use getCloudFoldersByConnectionId instead. */
 export function getCloudFolders(provider, folderId) {
   return request(`/api/cloud/folders/${provider}/${folderId}`)
 }
 
+/**
+ * Rename a cloud connection's display name.
+ */
+export function renameCloudConnection(id, displayName) {
+  return jsonRequest(`/api/cloud/connections/${id}`, 'PATCH', { display_name: displayName })
+}
+
 /**
  * Initiate OAuth flow for Google Drive or OneDrive.
  *