chore: import upstream snapshot with attribution

rules/python/coding-style.md

@@ -0,0 +1,42 @@
+---
+paths:
+  - "**/*.py"
+  - "**/*.pyi"
+---
+# Python Coding Style
+
+> This file extends [common/coding-style.md](../common/coding-style.md) with Python specific content.
+
+## Standards
+
+- Follow **PEP 8** conventions
+- Use **type annotations** on all function signatures
+
+## Immutability
+
+Prefer immutable data structures:
+
+```python
+from dataclasses import dataclass
+
+@dataclass(frozen=True)
+class User:
+    name: str
+    email: str
+
+from typing import NamedTuple
+
+class Point(NamedTuple):
+    x: float
+    y: float
+```
+
+## Formatting
+
+- **black** for code formatting
+- **isort** for import sorting
+- **ruff** for linting
+
+## Reference
+
+See skill: `python-patterns` for comprehensive Python idioms and patterns.