Move/copy messages (and other recordings) to another project #792

Use case

A common new-project setup flow: create a project (often from a template), then move existing messages from an intake/staging project into it. People are doing this with AI agents driving the CLI, and it's the step that can't be automated.

The web UI supports Move / Copy to another project for messages (and other recordings), but neither the CLI (v0.11.0) nor the public API exposes it:

• basecamp messages has list, show, create, update, publish, pin, unpin, trash, archive, restore — no move/copy
• PUT /messages/:id.json only accepts subject, content, category_id
• The only move endpoints in bc3-api are card/column moves and position endpoints

Current workaround and why it falls short

messages show → messages create in the target project → re-post comments → trash original. This loses the original author, timestamps, comment authorship, boosts and history, and re-notifies people.

Request

Something like:

basecamp messages move <id|url> --to <project> [--message-board <id>]
basecamp messages copy <id|url> --to <project>

(or a generic basecamp recordings move/copy), backed by a public API endpoint mirroring the web UI's Move/Copy.