Split engine and runtime entry points

Date: 2026-05-02 Area: runtime Pull Request: #493

Engine and runtime entry points are split explicitly. TGocciaEngine owns language execution, core built-ins, source strings/source lists, and Script-vs-Module entry semantics through SourceType; TGocciaRuntime owns host/runtime globals, special-purpose opt-ins such as test assertions/benchmarks/FFI, file-backed convenience helpers, and the default filesystem module content provider. GocciaScriptLoaderBare remains a core-engine-only frontend that can read file/stdin into source text without attaching runtime globals, and the CLI CI suite now covers that contract. architecture.md § Main Layers. embedding.md § Engine API.