Reduce Artifacts MCP surface to nine model tools

[nicosuave]

Artifacts advertises 48 model operations, so ordinary authoring includes tool definitions for scripts, files, schedules, plugins and native apps. This advertises nine model tools and retrieves advanced schemas on demand through the same connection. Definition size drops from 36.9 KB to 8.7 KB.

Keep artifact_guide, artifact_list, artifact_read, artifact_write, artifact_edit and artifact_open directly available. Add artifacts_discover for catalog search and exact schemas, artifacts_query for enforced reads, and artifacts_execute for actions. All 48 hosted operations remain reachable; existing direct calls and app-only gallery tools remain compatible. Each dispatched call uses the original schema and authorization path and preserves preview metadata, diagnostics and optimistic conflicts. Guide topics, plugin instructions and CI coverage follow the new interface.

Local validation:

• Both application and Cloudflare typechecks passed on current main.
• Authenticated official-SDK HTTP integration passed on the rebased branch: 4 tests / 166 assertions covering all 48 operations through one connection, native app deployment, ownership checks, schema/read-only rejection and real browser previews/completion.
• Local MCP regressions: 23 tests passed; plugin/discovery regressions: 22 passed; legacy HTTP compatibility: 2 passed; MCP App browser regressions: 20 passed.
• Installed tarball passed CLI, gallery and official-SDK stdio discovery/query/dispatched-preview checks outside the checkout. Default package build passed and excludes the test plugin.

Full repository, Docker and executable checks are left to PR CI. No production deployment or connection configuration change was performed.