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.

README.md

@@ -439,6 +439,8 @@ The classifier learns from you in three ways. Manually linking a merchant record
 
 **AI classification → Analyse** runs in the background: the page shows how many transactions have been analysed, proposed changes, and every per-transaction failure as it happens, with a **Stop** button that abandons the run without writing anything. You can navigate away and return; the run keeps building and the page re-attaches to it. A run that has produced no successful result and fails **three times in a row with the same error** stops early and reports that error — a wrong key or an unsupported model surfaces within seconds instead of repeating across the whole range.
 
+Wherever a category or tag is assigned — the transaction editor, an **Analyse** correction, or a merchant's defaults — the picker creates missing entries in place. Type a name and choose **Create "…" in …**: a bare name lands under the kind's root, and **Parent / Name** creates under that parent. New tags are typed next to the tag checkboxes. Assignment pickers offer leaf categories only, matching what the server accepts, and an existing name is selected rather than duplicated. Creating during an **Analyse** review keeps the preview applicable as long as the transactions themselves are unchanged.
+
 ## Data, backups, and recovery
 
 Back up the **entire canonical finance directory**, including registry files, journals, `config.toml` when present, and operational/recovery state, plus any separately stored environment-managed secrets. `state/openrouter.json` and `state/enablebanking.json` contain UI-managed credentials: protect backups accordingly, including the matching banking session state. Stop the service for a consistent filesystem backup. DuckDB under `cache/` can be excluded and rebuilt.