--situ/--affected emit run="python3 <file>" for Django/pytest test modules, which cannot be run that way

## What is wrong

`--situ` (and `--affected` under it) emits a `run=""` hint per test file. On a Django repo the hint is:

```
scheduler/tests/scheduler/test_smart_schedules.py [partner] [hops=1] (run: python3 scheduler/tests/scheduler/test_smart_schedules.py)
scheduler/tests/scheduler/test_battery_warming_schedules.py [hops=1] (run: python3 scheduler/tests/scheduler/test_battery_warming_schedules.py)
```

`python3 ` does not run a Django `TestCase` module. It imports Django models at module level with no settings configured and fails with `ImproperlyConfigured`. The correct runner is `pytest ` (a `pytest.ini`/`conftest.py` is present at the repo root) or `./manage.py test `.

The `ripwire-change-check` skill says "no `run=` means not derivable, never treat its absence as no runner". A wrong `run=` is worse than an absent one: an agent pastes it, gets a settings error, and may conclude the test is broken.

## Environment

ripwire 0.6.0 (built_from=2d2f10e62), macOS arm64. Django monolith, tests under `/tests/**/test_*.py`, `conftest.py` and `pytest.ini` at repo root.

## Suggestion

For Python test files, only emit `run=` when a runner is actually evidenced:

- `pytest.ini`, `pyproject.toml [tool.pytest.ini_options]`, `conftest.py`, or `setup.cfg [tool:pytest]` present at or above the test's directory: `run="pytest "`.
- `manage.py` present and the file imports `django`: `run="python manage.py test "`.
- Neither, and the file has no `if __name__ == "__main__"` block: omit `run=` rather than defaulting to `python3 `.

The same "is this file directly executable" check would also fix the hint for `unittest` modules without a main guard.

Trace the --situ and --affected entry points, then read the ripwire-change-check skill and inspect how run= hints are derived. Use pytest.ini, conftest.py, manage.py, and the referenced Django test modules as evidence cases; done means pytest or manage.py test is suggested when supported, and run= is omitted when no direct runner is evidenced.

Written by the indexing model from the issue text.