style: sort Python imports with isort

Add isort configuration (profile=black, line_length=100) to pyproject.toml,
add isort pre-commit hook, and auto-sort imports across all Python source files.

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

python/commands/board/layers.py

@@ -2,9 +2,10 @@
 Board layer command implementations for KiCAD interface
 """
 
-import pcbnew
 import logging
-from typing import Dict, Any, Optional
+from typing import Any, Dict, Optional
+
+import pcbnew
 
 logger = logging.getLogger("kicad_interface")