async_from 0.4.1

# Docs

### Scope

Design and API documentation for `async_from`.

### Responsibility Table

| File | Responsibility |
|--------|----------------|
| `feature/` | Feature scope, design rationale, and cross-references for user-facing capabilities |
| `api/` | Public trait contracts — operations, error handling, and compatibility guarantees |
| `invariant/` | Correctness properties with enforcement mechanism and violation consequences |
| `pattern/` | Architectural design patterns governing the API surface |
| `entities.md` | Cross-entity index of all doc entity types and doc instances |
| `doc_graph.yml` | Machine-readable cross-reference graph of all doc instances |