ADR-0001: Repository and Application Layout

Status: Accepted

Defines the monorepo structure with apps/backend (FastAPI/Python) and apps/web (React/Vite) as the two main application directories, plus shared packaging and CI infrastructure at the root.

Later change: ADR-0017 moved the backend to C# / .NET 10 in apps/server; the Python apps/backend directory was removed in #523.