feat(rpiv-pi): tier citation-floor findings so ambiguity and drift no longer halt runs

Every terminal ship cite-stop on record was an ambiguous-basename or
line-drift shape, never a fabrication. verifyCitations now marks those
resolver-limitation findings advisory; an advisory-only structure verdict
rates severity "low", which the gates' allDimensionsPass floor rides
through — ship's loop-less plan-cite-check gate stops only on a path
resolving to nothing or a files: coverage gap, and build/vet stop burning
fix rounds on path-prefix omissions. Ship's grade panel adjudicates the
surviving advisory findings: the correctness unit receives the floor's
verdict via the grade skill's new optional --cite-check flag and folds
each finding into its live-codebase spot-check under the existing
citation-resolution rule.