Rewrite ARCHITECTURE.md as a higher-level system document.
The new version removes file-by-file detail, adds mermaid diagrams,
and focuses on runtime boundaries, communication links, security,
state ownership, and cross-cutting concerns so readers can understand
how the app is architected without reading the code first.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Create ARCHITECTURE.md with a concrete overview of the Electron app,
its renderer/main/preload boundaries, shared domain model, .NET
sidecar, persistence model, workflow execution path, tooling model,
and build/release pipeline.
Also update AGENTS.md so future agents keep ARCHITECTURE.md in sync
when a change materially affects the system design.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
