The terminal's resilience screen sets or forgets where snapshots go, never showing a key, as MCP `backups_destination` does #7269

For: the owner setting up a fresh forge from the terminal: nothing is safe until snapshots leave the box. Never lost means that step is reachable from every door.

saveDestination and forgetDestination are reached from the Backups page and MCP backups_destination. The terminal's resilience screen (src/tui/screens/resilience.ts) only reads.

Done:

• [ ] The screen says where snapshots go now (kind and place) or that they stay on this box.
• [ ] d, for a forge admin who is a person, asks for endpoint, bucket, region, access key and secret key (the secret is masked as typed), validates them as the page does and saves; a refused field is named in the page's words.
• [ ] f forgets the destination after a confirm.
• [ ] A new test/tui-backups.test.ts: set, read back without a key, refuse a bad endpoint, forget; no frame ever contains the access or secret key.

Files: src/tui/screens/resilience.ts, one test. Risk: medium; keys must never reach a frame or a log.