feat(scoring): validate scenario matrix references known attributes/recipients

[dchaudhari7177]

What

forbidden and appropriate_flows are (attribute_name, recipient_id) pairs, but nothing checked those names actually exist in the scenario's attributes/recipients. A typo silently mis-scored, and the CLI KeyErrored on attr_by_name[attribute_name].

Adds validate_scenario(scenario) in scoring.py: it raises a clear ValueError naming any forbidden/appropriate_flows pair that references an unknown attribute or recipient (and lists the known names). score() calls it first, so a mis-authored scenario fails loud with a pointer to the typo instead of a deep KeyError or a silent wrong rate.

Acceptance criteria

• ✅ A scenario with a bad reference raises a clear error naming the offending pair.
• ✅ Valid scenarios are unaffected — CLUB_RESERVE_SCENARIO (and ALL_SCENARIOS) validate clean, and the existing smoke/report tests are untouched.

Tests

tests/test_validate_scenario.py: the built-in validates; unknown-attribute, unknown-recipient, and an appropriate_flows typo each raise a ValueError with the offending pair in the message; and score() rejects a mis-authored scenario. Full suite: 31 passed, ruff check clean.

Fixes #2

[bamdadd]

Thanks @dchaudhari7177 — this correctly implements #2 (clear ValueError naming the offending pair, validated on score(), meaningful tests). One formatting nit before merge: ruff format --check . wants to reformat the hand-wrapped for label, flows in ((...), (...)) tuple around src/context_leak/scoring.py:49-51. Run uv run ruff format . on the file and re-commit — no logic change — and it'll go green. Nice one.

[bamdadd]

Almost there @dchaudhari7177 — ruff-check/mypy/pytest all pass, but ruff format --check . still fails on src/context_leak/scoring.py (the for label, flows in ((...), (...)): tuple wants one item per line). Just run uv run ruff format on that file and re-push and it's green. Thanks!

[dchaudhari7177]

Done — ran ruff format on src/context_leak/scoring.py and re-pushed. ruff format --check ., ruff check ., and pytest are all green now. Thanks!