[FEATURE] Control marketplace auto-update through settings.json

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

With plugins not auto-updating by default and the only option to enable auto-update being in the TUI, claude can't set up auto-updating plugins for users via editing the settings.json

Proposed Solution

Include a settings.json setting for marketplace auto-update

Alternative Solutions

_No response_

Priority

Low - Nice to have

Feature Category

Configuration and settings

Use Case Example

I'm making a marketplace with a central skill that tells claude what other plugins to recommend users install, and I'd like them to be able to just say "yeah that sounds good, add it to my settings" and not have to worry about going into a TUI option to change the settings or skipping that and not getting updates

Additional Context

_No response_