export, import: an export that pours back into a workspace whole

An export used to lose what plain files cannot carry: dates, names as
typed, the boards. It now writes .workspace.json beside the tree (format
1), and an import that finds one restores them. The markdown stays
plain, so the archive still reads without the application.

POST /api/import (:import! / in the UI) imports at the root: each
top-level directory becomes a space, or merges into the space already
there by that name, with its board and cards and the diary role. With a
manifest, media/ comes back as embedded files rather than a folder, a
file whose name ends in .md stays a file, and empty folders come back.

Export claims every path in one set, folders, then documents, then
files, so a file named notes.md beside a document notes no longer makes
a duplicate entry that failed the whole zip. Links to folders are
rewritten like links to documents, in one regex pass per kind instead
of a replace per file and document. A sealed file that will not open
now fails the export instead of being left out silently. The temporary
zip is made in the data directory, not in /tmp.

web/src/lib/api.ts

@@ -72,10 +72,13 @@ export interface SharedDocument {
 
 /** What an import did, as `POST /api/nodes/{id}/import` reports it. */
 export interface ImportReport {
+  /** New spaces, made by an import at the root. */
+  spaces: number
   folders: number
   documents: number
   files: number
   links: number
+  cards: number
   skipped: string[]
 }
 
@@ -230,6 +233,13 @@ export const api = {
     return request<ImportReport>(`/nodes/${id}/import`, { method: 'POST', body: form })
   },
 
+  /** An `:export!` poured back in whole: its directories become spaces. */
+  importRoot: (files: File[]) => {
+    const form = new FormData()
+    for (const file of files) form.append('file', file, file.webkitRelativePath || file.name)
+    return request<ImportReport>('/import', { method: 'POST', body: form })
+  },
+
   createNode: (input: {
     parent_id: number
     kind?: NodeKind