Problem
There is no visual, repo-local architecture overview that explains how Canton participant nodes interact via synchronization domains and how cross-domain workflow composition works.

Proposal

• Add docs/architecture/overview.md with a Mermaid diagram and a short description.
• Link this page from README.md (Architecture section).

Scope

• Docs-only change. No code or build files touched.

Rationale

• Easier onboarding for new contributors/integrators.
• Keeps a canonical high-level picture in-repo (alongside external docs).