Make `--name` create or resume a session

Describe the feature or problem you'd like to solve

copilot --name <name> creates a new named session, but it does not resume an existing session with that name. After the first launch, users and automation must know whether the session exists before selecting --name <name> or --resume <name>.

The same distinction breaks CLI relaunches. A session started with copilot --name project-a can fail during /update when the replacement process receives both the original --name and an internal --session-id:

error: option '-n, --name <name>' cannot be used with option '--session-id <id>' when it resolves to an existing or remote session or task.
--name only names a brand-new session created by --session-id=<new-uuid>; the resolved session was not renamed.

Proposed solution

Give copilot --name <name> create-or-resume behavior. --name should use the same name lookup and matching rules as --resume <name>:

1. If no session matches, create a session with that name.
2. If exactly one session matches, resume that session.
3. If multiple sessions match, follow the current --resume <name> ambiguity behavior. Do not create another session.
4. Resume the selected session when /restart, /update, or another command relaunches the CLI. A retained --name should not fail because the session now exists or because the relaunch also carries an internal session ID.

--resume should remain available for three uses: session IDs, the session picker, and existing workflows. Users and automation could then use one repeatable command whenever a stable name identifies the session.

Example prompts or workflows

1. The first copilot --name project-a invocation creates a named session.
2. A later copilot --name project-a invocation resumes that session.
3. /update or /restart resumes that session without a flag conflict.
4. An alias or script can keep invoking copilot --name project-a without first querying session state.

Additional context

Issue https://github.com/github/copilot-cli/issues/3332 reports /restart failing in a session created with --name. The requested semantics address that failure and the broader need for one repeatable name-based command.

Bắt đầu bằng cách lần theo cách CLI xử lý --name và --resume, sau đó kiểm tra các đường dẫn khởi chạy lại được /restart và /update sử dụng. So sánh hành vi với issue #3332 và xác minh bốn trường hợp được đề xuất: tạo khi không có kết quả khớp, tiếp tục khi có một kết quả khớp, giữ nguyên cách xử lý mơ hồ hiện tại và tránh xung đột trong khi khởi chạy lại.