Merge local plugins into plugin search results

[copyberry]

Merge local plugins into plugin search results

What changed

• Discover plugins from configured and repository marketplaces using the request's cwds, and merge up to 100 ranked local matches into the first remote result page.
• Match local plugin names, display names, and keywords without case or punctuation sensitivity, while applying global, personal, and workspace scope semantics.
• Deduplicate local and remote copies, preserve local installation metadata on the remote result, and treat the remote global catalog as authoritative over the local curated marketplace.
• Keep local search available for API-key authentication and when remote_plugin is disabled, and consistently report enabled: false because search results describe discovery rather than effective activation.

Testing

• Add coverage for merged pagination and ranking, API-key local search, scope and feature behavior, deduplication, installed state, and explicit disabled-state reporting.

[github-actions]

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