User messages are persisted with a `workflow` field
(backend/src/routes/chat.ts, projectChat.ts) and it is read back when
rendering chat history (ChatView -> UserMessage) to show which workflow a
message was sent under. But the column is never created by schema.sql or any
migration, so every user-message insert fails with PostgREST PGRST204
("Could not find the 'workflow' column of 'chat_messages'") and is dropped
silently (the insert result is not checked). The assistant insert has no
workflow column, so it succeeds — the net effect on a self-hosted install is
that reloading a thread shows the assistant reply but not the user's prompt.
Add the `workflow jsonb` column to schema.sql (fresh installs) and a
migration (existing installs), mirroring the adjacent content/files jsonb
columns.
