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

pyproject.toml

@@ -0,0 +1,72 @@
+[build-system]
+requires = ["setuptools>=61.0", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "fluency-cad"
+version = "2.0.0"
+description = "Parametric CAD application with OpenCASCADE geometry kernel"
+readme = "README.md"
+license = {text = "MIT"}
+requires-python = ">=3.10"
+authors = [
+    {name = "Fluency CAD Team"}
+]
+keywords = ["cad", "parametric", "opencascade", "3d-modeling"]
+classifiers = [
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "Intended Audience :: End Users/Desktop",
+    "License :: OSI Approved :: MIT License",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Topic :: Scientific/Engineering :: CAD",
+]
+
+dependencies = [
+    "cadquery>=2.4",
+    "ocp>=7.9.3",
+    "pygfx>=0.7.0",
+    "wgpu>=0.19.0",
+    "PySide6>=6.9.0",
+    "numpy>=2.2.0",
+    "scipy>=1.15.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0",
+    "black>=24.0",
+    "mypy>=1.8",
+    "ruff>=0.4.0",
+]
+
+[project.scripts]
+fluency-cad = "fluency.main:main"
+
+[project.urls]
+Homepage = "https://github.com/fluency-cad/fluency"
+Documentation = "https://github.com/fluency-cad/fluency#readme"
+Repository = "https://github.com/fluency-cad/fluency"
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.setuptools.package-data]
+fluency = ["py.typed", "*.pyi"]
+
+[tool.black]
+line-length = 100
+target-version = ["py310", "py311", "py312"]
+
+[tool.ruff]
+line-length = 100
+target-version = "py310"
+
+[tool.mypy]
+python_version = "3.10"
+warn_return_any = true
+warn_unused_configs = true
+disallow_untyped_defs = true