v0.2.4 — selfcheck provider preflight

• selfcheck UX: veracium selfcheck now preflights the provider — a
  missing SDK or missing ANTHROPIC_API_KEY exits with one clear install
  hint instead of a traceback or, worse, a garbage FAIL … injection asserts=1 scorecard (an erroring check was conservatively scored as an
  assert, which read exactly like the injection guarantee failing). If the
  provider fails every check mid-run (e.g. bad credentials), the result is
  now reported as DID NOT RUN (exit code 2) — an environment problem is
  never rendered as a memory-safety result.