The terminal's boards screen makes a board with `n`, duplicates one with `c` and deletes one with `D` and a confirm, as the /boards page does #7319

Intent: a forge admin shapes their boards from the terminal, not only reads them.

Done:

• [ ] On the boards list (src/tui/screens/boards.ts), n asks for a title and calls makeBoard (src/actions/boards.ts); the new board opens.
• [ ] c on a row calls duplicateBoard; D asks delete <title>? y/n and calls deleteBoard.
• [ ] Every refusal (an empty or too-long title, not an admin, not found) is shown in the action's words, and nothing changes.
• [ ] The key bar lists the three keys.
• [ ] test/tui-boards.test.ts gains cases that make, duplicate and delete a board and see the list change, and one where a non-admin is refused.

Files: src/tui/screens/boards.ts, test/tui-boards.test.ts.