Expose discoverability and full share principals in share context, carry
roles through save/updateTargets, hydrate local shared plugin reads, and
keep share URLs only under plugin.shareContext.
Requires discoverability on plugin/share/updateTargets so the server can
manage workspace link access consistently, including auto-adding the
workspace principal for UNLISTED.
Also rejects LISTED on share creation and blocks client-supplied
workspace principals while preserving response parsing for LISTED.
Extends `plugin/share/save` to accept optional discoverability and
shareTargets while uploading plugin contents, and adds
`plugin/share/updateTargets` for share-only target updates without
re-uploading.
