feat: Replace SDF kernel with OpenCASCADE, VTK with pygfx

Major architecture migration:

- Remove SDF-based geometry kernel (sdf/)
- Remove VTK renderer (drawing_modules/)
- Remove old mesh modules (mesh_modules/)

New components:
- geometry/base.py: Abstract geometry kernel interface
- geometry_occ/kernel.py: OpenCASCADE implementation via CadQuery/OCP
- geometry_occ/sketch.py: 2D sketching with constraint solving
- rendering/base.py: Abstract renderer interface
- rendering/pygfx_renderer.py: WebGPU-based renderer
- models/data_model.py: Project, Component, Sketch, Body classes
- main.py: New Qt-based application

Features:
- STEP/IGES import/export
- Exact BRep geometry (vs approximate SDF mesh)
- Parametric sketching with constraints
- Boolean operations (union, difference, intersection)
- Fillet and chamfer operations
- Modern pygfx renderer (~30MB vs VTK ~200MB)

Dependencies:
- cadquery >= 2.4
- ocp >= 7.9.3
- pygfx >= 0.7.0
- wgpu >= 0.19.0
- PySide6 >= 6.9.0

README.md

@@ -0,0 +1,112 @@
+# Fluency CAD 2.0
+
+A parametric CAD application built on OpenCASCADE Technology (OCCT) with a modern pygfx-based 3D renderer.
+
+## Features
+
+- **OpenCASCADE Geometry Kernel**: Industry-standard BRep geometry with exact precision
+- **STEP/IGES Import/Export**: Full support for industry-standard CAD file formats
+- **Parametric Sketching**: 2D sketching with constraint solving using CadQuery
+- **Boolean Operations**: Union, difference, and intersection
+- **Fillet & Chamfer**: Apply edge treatments to solid bodies
+- **Modern Renderer**: WebGPU-based rendering with pygfx (smaller footprint than VTK)
+
+## Architecture
+
+```
+fluency/
+├── src/fluency/
+│   ├── geometry/           # Geometry abstraction layer
+│   │   └── base.py         # Abstract interfaces
+│   ├── geometry_occ/       # OpenCASCADE implementation
+│   │   ├── kernel.py       # OCGeometryKernel
+│   │   └── sketch.py       # OCCSketch with constraints
+│   ├── rendering/          # Rendering abstraction
+│   │   ├── base.py         # Abstract renderer
+│   │   └── pygfx_renderer.py
+│   ├── models/             # Data models
+│   │   └── data_model.py   # Project, Component, Sketch, Body
+│   └── main.py             # Application entry point
+├── tests/
+│   └── test_geometry.py
+└── pyproject.toml
+```
+
+## Installation
+
+```bash
+# Create virtual environment
+python -m venv .venv
+source .venv/bin/activate  # On Windows: .venv\Scripts\activate
+
+# Install dependencies
+pip install -e ".[dev]"
+```
+
+## Dependencies
+
+| Package | Purpose |
+|---------|---------|
+| cadquery | High-level OpenCASCADE Python bindings |
+| ocp | Low-level OpenCASCADE Python bindings |
+| pygfx | WebGPU-based 3D renderer |
+| wgpu | WebGPU Python bindings |
+| PySide6 | Qt GUI framework |
+| numpy | Numerical computing |
+| scipy | Scientific computing |
+
+## Usage
+
+```bash
+# Run the application
+fluency-cad
+
+# Or directly
+python -m fluency.main
+```
+
+## API Example
+
+```python
+from fluency.geometry_occ.kernel import OCGeometryKernel
+from fluency.geometry.base import Point2D
+
+# Create kernel
+kernel = OCGeometryKernel()
+
+# Create a sketch
+points = [
+    Point2D(0, 0),
+    Point2D(10, 0),
+    Point2D(10, 10),
+    Point2D(0, 10),
+]
+polygon = kernel.create_polygon(points)
+
+# Extrude to 3D
+body = kernel.extrude(polygon, height=20.0)
+
+# Apply fillet
+body = kernel.fillet(body, radius=2.0)
+
+# Export to STEP
+kernel.export_step(body, "part.step")
+
+# Export to STL
+kernel.export_stl(body, "part.stl")
+```
+
+## Comparison: Before vs After
+
+| Aspect | Before (SDF + VTK) | After (OCC + pygfx) |
+|--------|-------------------|---------------------|
+| Geometry Precision | Approximate (mesh) | Exact (BRep) |
+| Export Formats | STL only | STEP, IGES, STL, BREP |
+| File Size | Large (mesh) | Small (BRep) |
+| Fillet/Chamfer | Approximate | Exact |
+| Dependency Size | ~200MB (VTK) | ~30MB (pygfx) |
+| Constraint Solver | SolveSpace (separate) | CadQuery (integrated) |
+
+## License
+
+MIT License