[autodev] fix csv_reporter --csv collision with pytest-csv

Subprocess-spawned tests in e2e/_unit_tests/reporting/ crashed with
"argparse.ArgumentError: argument --csv: conflicting option string: --csv"
because pytest-csv (autoloaded via entry-point) and our custom plugin both
register --csv. pytest's option registry does not allow overrides.

Fix: drop pytest-csv from e2e/runner/requirements.txt. It was unused, dead
weight, and incompatible with pytest 9.x (uses removed hookwrapper marker).
Update conftest + csv_reporter comments to match.

After fix: 1229/1229 in e2e/_unit_tests pass.

Bug ticket creation deferred (user skipped interactive Q this session) —
payload recorded in _docs/_process_leftovers/2026-05-17_csv_reporter_*.md
for replay on next /autodev.

Co-authored-by: Cursor <cursoragent@cursor.com>

e2e/runner/conftest.py

@@ -206,8 +206,10 @@ def mock_suite_sat_url() -> str:
 
 # The CSV reporter plugin is a separate module so the unit tests can exercise
 # it directly without going through a real pytest run. It is registered via
-# `pytest_plugins` so docker-compose's `--csv=...` flag binds to our column
-# set rather than the upstream pytest-csv default.
+# `pytest_plugins` to provide the `--csv` / `--csv-columns` CLI surface used
+# by docker-compose. The upstream `pytest-csv` package is intentionally NOT a
+# dependency — its `--csv` flag would conflict with ours (pytest does not
+# allow option overrides) and it is incompatible with pytest 9.x.
 pytest_plugins = [
     "runner.reporting.csv_reporter",
     "runner.reporting.evidence_bundler",