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

.idea/workspace.xml

@@ -4,11 +4,31 @@
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-    <list default="true" id="8f0bafd6-58a0-4b20-aa2b-ddc3ba278873" name="Changes" comment="- added sdf folder ( doesnt work via pip or git=)">
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+      <change afterPath="$PROJECT_DIR$/doc/SELECTION_DELETION.md" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/doc/SINGLE_WINDOW_MIGRATION_PLAN.md" afterDir="false" />
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+      <change afterPath="$PROJECT_DIR$/drawing_modules/vtk_sketch_widget.py" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/drawing_modules/workplane.py" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/minimal_main.py" afterDir="false" />
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+      <change afterPath="$PROJECT_DIR$/test_delete_functionality.py" afterDir="false" />
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@@ -59,12 +79,14 @@
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@@ -81,13 +103,14 @@
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@@ -252,7 +275,15 @@
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@@ -287,6 +318,7 @@
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+    <MESSAGE value="- Improved sketching" />
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