Close instance ports from the CLI

[callen-bot]

Summary

• add brev ports close <instance-or-node> with a remove alias
• present an interactive picker for human use and support exact --id <port_id> --approve targeting for automation
• add --all to close every current mapping, with confirmation unless --approve is supplied
• support managed instances and registered nodes, including partial-failure reporting

Why

PR #441 adds the read layer and PR #442 adds the create layer. This stacked follow-up completes the delete layer for port mappings.

Impact

Users can remove one selected mapping, deterministically remove one mapping by its unique API ID, or remove all mappings in a single command.

Stack

• Base: Create instance ports from the CLI #442
• This PR: delete/close operations
• Follow-up: Update instance ports from the CLI #447 adds true in-place update/edit operations

Validation

• go test -race ./pkg/cmd/ports ./pkg/cmd/util ./pkg/cmd
• make fmtcheck
• make vet
• make lint
• make fast-build
• bash -n test-ports-e2e.sh