AD-1201: Add MCP tool registry

[alph-cmky]

Summary

• Extend the development backlog with Phase 12 MCP tooling tasks.
• Add a controlled MCP tool registry abstraction with discoverable tool metadata and input schemas.
• Add read-only tools for listing agents, listing workflows, and getting workflow details.
• Reject unknown tools and missing workflows with clear errors.
• Export MCP registry APIs and add workspace dependencies on server/workflow-core types.

Testing

• TDD red check: pnpm test packages/mcp-server/src/tool-registry.test.ts initially failed because tool-registry.js did not exist.
• pnpm test packages/mcp-server/src/tool-registry.test.ts
• pnpm lint && pnpm format && pnpm typecheck && pnpm test && pnpm build

Stacked on #54.