Create instance ports from the CLI

[callen-bot]

Summary

• add brev ports open <instance-or-node> <port> with an add alias
• create raw TCP, UDP, and SSH mappings with repeatable --allow <CIDR>
• create HTTP/HTTPS application endpoints with --public, repeatable --authorize, and --hostname
• support managed instances and registered nodes, with table or stable JSON output

Why

PR #441 exposes existing mappings. This stacked follow-up adds the create flows, including the same HTTP application-port creation used by the UI.

Impact

Users can expose raw services or HTTP applications from the terminal, configure source or authorization access during creation, and capture the unique port_id for automation.

Stack

• Base: Add ports command for instances and nodes #441
• This PR: create/open operations
• Follow-up: delete/close operations

Validation

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