Story-1736 - functions lane - BDD freshness

check:features gate

This Story turns pytest-bdd feature files into CI-checked contracts instead of prose that can silently drift away from Python step bindings.

The mental model: the feature file is a hearing transcript, and the step module is the sworn witness list. The gate fails when the transcript names a witness nobody can call, when someone marks the hearing as work-in-progress, or when a skipped answer tries to count as testimony.

What changed

scripts/check_features.py scans required features for @wip.
The same script runs pytest --generate-missing --feature tests/features tests/steps so unbound scenarios and undefined steps fail before the full suite.
It then executes tests/steps and rejects skipped, xfailed, or xpassed BDD outcomes.
CI runs the new named check:features step before the normal full test suite.

Proof fixture

tests/feature_gate_fixtures/ contains a deliberately incomplete feature binding outside the required suite. The unit proof runs the gate against that non-required path and asserts it exits non-zero with pytest-bdd's missing-step message.

python scripts/check_features.py \
  --features tests/feature_gate_fixtures \
  --steps tests/feature_gate_fixtures/missing_step_probe.py

How to verify

python scripts/check_features.py passes for the required BDD suite.
The proof command above fails on the deliberate missing step.
pytest tests/ and Ruff on the new Python files stay green.

Story-1736 walkthrough for pramaan-functions. Issue: pramaan-spec#1736.