- journal.Plugin.MCP: list_posts, show_post, list_categories, list_tags,
create_post, update_post, delete_post and the draft_post prompt, guard
backend, listed with golem15.journal.access_posts; update fields are
optional so only sent keys reach the route
- optionalBackendPrincipal honours the MCP dispatch marker (no bearer
short-circuit; anonymous reads unchanged)
- require summercms v0.4.4
- TestJournalMCPSmoke, TestOptionalBackendPrincipalDispatch