The fixture chats leave the real database, archived first

A test wrote 204 fixture chats of 1,000 messages each into the real web.db. Approved: fix the leaking test first, then ARCHIVE (export to a file, proven row by row) and REMOVE them from the live database. This is the ONE exception to “the conversation record is never removed”: only trashed conversations, only after a verified archive and a verified pre-archive copy, only from the shell with the server stopped, all or none (npm run db-archive, the action database.conversations.archive). Any other removal needs a decision of its own.