Reorganized the application around a clear frontend/backend boundary.

src/bedit/
├── __main__.py
├── core/                   # Pure Python, no PySide
│   ├── model.py
│   ├── port_types.py
│   ├── serializer.py
│   └── libraries.py
└── gui/                    # All Qt-dependent code
    ├── app.py
    ├── main_window.py
    ├── preferences.py
    ├── controllers/
    ├── dialogs/
    ├── graphics/
    ├── models/
    └── generated/          # Designer/resource output only
Notable improvements:
Domain models, serialization, port types, and library parsing are now Qt-free.
Qt signals and undo infrastructure are explicitly isolated under gui/controllers.
Library parsing is separated from the Qt repository and tree models.
All generated Python is contained in gui/generated.
Designer build tasks now write to the generated directory.
The application entry point and package metadata use the new paths.
README now documents the structure and dependency rules.
Removed the old mixed document, library, and workspace packages.

BEdit/src/bedit/gui/models/__init__.py

@@ -0,0 +1 @@
+"""Qt model/view adapters and repositories."""