re-org en App

lib/src/core/README.md

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+# Core Module — Manager and Executor Layers
+
+## Overview
+
+The `core` module contains two architectural layers that drive rendering:
+
+| File | Responsibility |
+|------|---------------|
+| **context** | **Manager layer** — owns GPU hardware resource lifecycle (Instance, Surface, Adapter, Device, Queue). Initializes GPU at startup; orchestrates frame-by-frame rendering via begin_frame() / end_frame(). Does not own rendering logic. |
+| **renderer** | **Executor layer** — owns Device/Queue references after initialization from Context. Orchestrates draw calls by binding Material pipelines and Mesh vertex data into a RenderPass. Does not own raw hardware resources externally or RenderPipelines/shaders. |
+| **frame** | Per-frame RAII wrapper around the surface texture and its TextureView. Exists only for the duration of a single rendering pass. |
+
+## Interaction with Other Modules
+
+- **utils**: Context returns WsgError from all fallible methods; Renderer does not use errors directly.
+- **pipeline**: Context requires Device reference during pipeline creation in new(); Renderer uses PipelineCache indirectly through Material.
+- **resources**: Renderer consumes Mesh and Material instances for draw calls.
+- **scene**: Renderer queries Scene for Material/Mesh pairs to render.