style: apply Black formatting to all Python files

Add [tool.black] config to pyproject.toml and Black hook to
.pre-commit-config.yaml (rev 26.3.1), then auto-format all Python
source and test files with line-length=100, target-version=py310.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_platform_helper.py

@@ -3,6 +3,7 @@ Tests for platform_helper utility
 
 These are unit tests that work on all platforms.
 """
+
 import pytest
 import platform
 from pathlib import Path
@@ -176,6 +177,7 @@ class TestKiCADPathDetection:
         PlatformHelper.add_kicad_to_python_path()
         try:
             import pcbnew
+
             # If we get here, pcbnew is available
             assert pcbnew is not None
             version = pcbnew.GetBuildVersion()