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

tests/test_geometry.py

@@ -0,0 +1,187 @@
+"""Tests for Fluency CAD geometry kernel."""
+
+import pytest
+import numpy as np
+
+from fluency.geometry_occ.kernel import OCGeometryKernel, OCCGeometryObject
+from fluency.geometry_occ.sketch import OCCSketch
+from fluency.geometry.base import Point2D
+
+
+class TestOCGeometryKernel:
+    """Tests for the OpenCASCADE geometry kernel."""
+
+    def test_kernel_creation(self):
+        """Test kernel can be created."""
+        kernel = OCGeometryKernel()
+        assert kernel is not None
+
+    def test_create_point(self):
+        """Test point creation."""
+        kernel = OCGeometryKernel()
+        point = kernel.create_point(10.0, 20.0)
+        assert point is not None
+
+    def test_create_line(self):
+        """Test line creation."""
+        kernel = OCGeometryKernel()
+        start = Point2D(0, 0)
+        end = Point2D(10, 10)
+        line = kernel.create_line(start, end)
+        assert line is not None
+
+    def test_create_circle(self):
+        """Test circle creation."""
+        kernel = OCGeometryKernel()
+        center = Point2D(0, 0)
+        circle = kernel.create_circle(center, 5.0)
+        assert circle is not None
+
+    def test_create_rectangle(self):
+        """Test rectangle creation."""
+        kernel = OCGeometryKernel()
+        rect = kernel.create_rectangle(10.0, 20.0)
+        assert rect is not None
+
+    def test_create_polygon(self):
+        """Test polygon creation."""
+        kernel = OCGeometryKernel()
+        points = [
+            Point2D(0, 0),
+            Point2D(10, 0),
+            Point2D(10, 10),
+            Point2D(0, 10),
+        ]
+        polygon = kernel.create_polygon(points)
+        assert polygon is not None
+
+    def test_extrude_polygon(self):
+        """Test extruding a polygon."""
+        kernel = OCGeometryKernel()
+        points = [
+            Point2D(0, 0),
+            Point2D(10, 0),
+            Point2D(10, 10),
+            Point2D(0, 10),
+        ]
+        polygon = kernel.create_polygon(points)
+        extruded = kernel.extrude(polygon, 20.0)
+        assert extruded is not None
+
+    def test_get_mesh(self):
+        """Test mesh generation."""
+        kernel = OCGeometryKernel()
+        points = [
+            Point2D(0, 0),
+            Point2D(10, 0),
+            Point2D(10, 10),
+            Point2D(0, 10),
+        ]
+        polygon = kernel.create_polygon(points)
+        extruded = kernel.extrude(polygon, 20.0)
+
+        vertices, faces = kernel.get_mesh(extruded)
+
+        assert len(vertices) > 0
+        assert len(faces) > 0
+        assert vertices.shape[1] == 3
+        assert faces.shape[1] == 3
+
+    def test_get_bounding_box(self):
+        """Test bounding box calculation."""
+        kernel = OCGeometryKernel()
+        points = [
+            Point2D(0, 0),
+            Point2D(10, 0),
+            Point2D(10, 10),
+            Point2D(0, 10),
+        ]
+        polygon = kernel.create_polygon(points)
+        extruded = kernel.extrude(polygon, 20.0)
+
+        min_pt, max_pt = kernel.get_bounding_box(extruded)
+
+        assert min_pt.x <= max_pt.x
+        assert min_pt.y <= max_pt.y
+        assert min_pt.z <= max_pt.z
+
+    def test_get_volume(self):
+        """Test volume calculation."""
+        kernel = OCGeometryKernel()
+        points = [
+            Point2D(0, 0),
+            Point2D(10, 0),
+            Point2D(10, 10),
+            Point2D(0, 10),
+        ]
+        polygon = kernel.create_polygon(points)
+        extruded = kernel.extrude(polygon, 20.0)
+
+        volume = kernel.get_volume(extruded)
+
+        assert volume > 0
+        assert abs(volume - 2000.0) < 0.1
+
+
+class TestOCCSketch:
+    """Tests for the OpenCASCADE sketch."""
+
+    def test_sketch_creation(self):
+        """Test sketch can be created."""
+        sketch = OCCSketch()
+        assert sketch is not None
+
+    def test_add_point(self):
+        """Test adding a point."""
+        sketch = OCCSketch()
+        point = sketch.add_point(10.0, 20.0)
+        assert point is not None
+        assert point.entity_type == "point"
+
+    def test_add_line(self):
+        """Test adding a line."""
+        sketch = OCCSketch()
+        p1 = sketch.add_point(0, 0)
+        p2 = sketch.add_point(10, 10)
+        line = sketch.add_line(p1, p2)
+        assert line is not None
+        assert line.entity_type == "line"
+
+    def test_add_circle(self):
+        """Test adding a circle."""
+        sketch = OCCSketch()
+        center = sketch.add_point(0, 0)
+        circle = sketch.add_circle(center, 5.0)
+        assert circle is not None
+        assert circle.entity_type == "circle"
+
+    def test_add_rectangle(self):
+        """Test adding a rectangle."""
+        sketch = OCCSketch()
+        entities = sketch.add_rectangle((0, 0), (10, 10))
+        assert len(entities) == 8
+
+    def test_get_points(self):
+        """Test getting points."""
+        sketch = OCCSketch()
+        sketch.add_point(0, 0)
+        sketch.add_point(10, 10)
+        sketch.add_point(20, 20)
+
+        points = sketch.get_points()
+        assert len(points) == 3
+
+    def test_clear(self):
+        """Test clearing sketch."""
+        sketch = OCCSketch()
+        sketch.add_point(0, 0)
+        sketch.add_point(10, 10)
+
+        sketch.clear()
+
+        points = sketch.get_points()
+        assert len(points) == 0
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])