Create categories and tags in place from every assignment picker

Category and tag inputs across the transaction editor, Analyse
corrections, and merchant defaults now mint missing entries without a
detour through the registry pages. A bare name lands under the kind's
root, "Parent / Name" targets that parent, and typing an existing name
selects it instead of duplicating. Enter only creates when nothing
matches, server rejections surface inline in the dropdown, and
assignment pickers offer leaf categories only — the shape the server
validates.

Mutations now return the accepted state so callers can select the id
the server just minted, and the revision-keyed remounts on Transactions
and the registry pages are gone: they closed the open modal and threw
away pending edits the moment any in-modal creation committed.

OPERATIONS.txt

@@ -13,7 +13,12 @@ from Accounts and confirm the reviewed mapping. The application starts empty
 except for expense/income fallback categories. Create your category tree, tags,
 and merchants in the UI. Enable a merchant's default rule explicitly only when
 its category/tags are reliable; leave it disabled for ambiguous merchants such
-as Amazon.
+as Amazon. Category and tag pickers create in place: type an unknown name in
+a category picker and choose "Create … in …" (a bare name lands under the
+kind's root; "Parent / Name" targets that parent), or type a new tag next to
+the tag checkboxes. Assignment pickers offer leaf categories only, matching
+what the server accepts; a name that already exists is selected, never
+duplicated.
 
 Tests: go test ./...
 The Go build embeds web/dist, so build React first. CGO and a C++ linker are