Plugin/marketplace requests distinguish missing scope from not entitled

What

• Installing a plugin now fails with a clear message when your claude.ai login hasn't been granted plugin access yet: "The plugin archive was not downloaded: this claude.ai login has not been granted plugin access yet. Start Claude Code interactively once, then try again."
• Listing plugins, and other plugin/marketplace metadata lookups, now recognize a distinct "no scope" condition (as opposed to being flatly not entitled) and degrade gracefully with a skipped result instead of throwing or reporting the wrong reason.
• Plugin/marketplace sync now treats a non-interactive authentication failure as lacking the user:plugins scope, short-circuiting with "claude.ai login lacks the user:plugins scope in this session".
• The background flow that silently re-requests an OAuth token with the extra user:plugins scope now skips itself when running in a non-interactive session (except inside the VS Code extension), instead of failing in a confusing way.

Why Previously these failures could look like generic errors or the wrong entitlement message. Now Claude Code tells you specifically that your login session needs to be granted plugin access, and points you to the fix (start Claude Code interactively once), rather than leaving plugin installs or syncs failing mysteriously in non-interactive environments.