feat(settings): read and update server settings

[tarik02]

Problem

The CLI cannot inspect or automate the durable server settings owned by a T3 Code environment.

Scope

Add:

• settings get
• settings update --patch <json>
• settings update --stdin

The update command must accept exactly one patch source and decode the full value with the T3 Code ServerSettingsPatch schema before dispatch.

Acceptance criteria

• settings get prints the complete server settings as JSON.
• settings update supports nested objects, arrays, booleans, and nullable values without a custom dotted-key language.
• The command prints the complete updated settings returned by the server.
• Invalid patches fail locally with a useful schema error.
• Inline JSON and stdin produce identical requests.

Out of scope

• A named CLI flag for every setting.
• Dotted key/value path syntax.