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/test_ipc_backend.py

@@ -14,8 +14,8 @@ Usage:
     ./venv/bin/python python/test_ipc_backend.py
 """
 
-import sys
 import os
+import sys
 
 # Add parent directory to path
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))