nodes: a write changes only what it sends

`PUT /api/nodes/{id}` wrote the whole node, and a field left out was taken as
empty: a rename sent without the body erased the text. The browser always sent
it, which was the other half of the trouble. To rename a document it sent the
body it had — the draft for one open here, a copy fetched a moment earlier for
any other — and without the version it had seen, so a save made in another
tab, on the phone or over the mount in between was written over, kept only as
a revision nobody was told about.

Now `name` and `body`, like the rest, change only when they are sent. A rename
sends the name alone, and for a document open in a tile the `updated_at` that
tile last saw, so a rename of a document saved elsewhere since is refused the
way `:w` is, rather than stamping a new version over it that the next autosave
would then write the draft past. Toggling a space's board sends only that.

web/src/lib/api.ts

@@ -478,6 +478,7 @@ export const api = {
     request<{ prev: DiaryEntry | null; next: DiaryEntry | null }>(`/diary/around/${id}`),
 
   /**
+   * Only what is sent changes: a rename sends the name alone.
    * `base_updated_at`: refused with 409 if the node was saved since then.
    * `restore`: the text is a revision brought back, so what it replaces is
    * kept as a revision whatever the last one was.
@@ -485,8 +486,8 @@ export const api = {
   updateNode: (
     id: number,
     input: {
-      name: string
-      body: string
+      name?: string
+      body?: string
       created_at?: number
       has_board?: boolean
       base_updated_at?: number