Add per-deploy-request aggressive cutover

[mscoutermarsh]

Summary

Opt a single Vitess deploy request into aggressive cutover without changing the database setting or other deploy requests.

• pscale deploy-request create --aggressive-cutover sends aggressive_cutover: true only when the flag is set.
• pscale deploy-request update --aggressive-cutover and --aggressive-cutover=false PUT .../deploy-requests/:number/aggressive-cutover with { "enable": <bool> }. Unset flags are not sent.
• show and queue human tables include an aggressive_cutover column. JSON output already prints the deployment field from the API object.
• AGENTS.md documents the flags next to the other deploy-request commands.

Database aggressive-cutover and deploy-request force-cutover are unchanged. There is no confirmation prompt.

Test plan

• go test ./internal/cmd/deployrequest/ ./internal/planetscale/ -count=1
• Create with --aggressive-cutover against an API that accepts the field and confirm deployment.aggressive_cutover is true
• Update with --aggressive-cutover=false while the request is still editable, then again after submission and confirm the 422 is printed