Add v3.0.0 agent manifest integration

## Summary
- Add ToolRegistry.fromManifest() for agent manifest tool config
- Add AgentToolsServer.fromManifest() convenience method
- Export ToolRegistry from index.mjs

## Files
- Modified: src/registry/ToolRegistry.mjs
- Modified: src/AgentToolsServer.mjs
- Modified: src/index.mjs