Add registry client that queries Official, Glama, and Smithery MCP
registries with caching, request deduplication, retry logic, and
result ranking/dedup. Includes 53 tests covering all components.
Also fix null priority values in cancelled tasks (19-21) that broke
Task Master, and add new tasks 25-27 for registry completion and
CLI discover/install commands.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
