[thorwhalen]

Closes #156.

read-ci-config, set-env-vars and build-dist now run their script by path from the action's own checkout ($GITHUB_ACTION_PATH/../../wads/scripts/...), as export-ci-env and install-system-deps already do. The pip install 'wads>=0.1.48' steps are gone. The scripts load wads/ci_config.py through a small stdlib-only loader (wads/scripts/_checkout_import.py) so they never import the wads package (which needs third-party deps) or a stale wheel. Backward compatible: python -m wads.scripts.* still works.

Tests: new test_actions_run_from_checkout.py (no pip install in the actions; scripts run under python -I [-S] without the wads package); test_action_definitions updated to the path form. Full suite green except test_stub_transport_default::test_rerendering_json_stub_content_converts_it_to_named, which fails identically on master (macOS File name too long, unrelated).

Review (fresh Opus adversarial): found that the old pip install silently supplied packaging, so the #59 test-extra warning would have vanished; fixed by installing packaging in read-ci-config, with a test that asserts the warning and outputs under python -I. Also fixed stale comments, strengthened tests. Declined as not worth it: sys.path tidy-up (harmless), wider refactor (loader is 28 lines, no bloat). Deferred nit: docs snippets in wads/scripts/README.md still show -m form.