scoring: classify evidence-based abstentions without survey truth #115

The truth != unknown guard also skips abstention classification. In the fixture photo-depth/c2-pool, failed evidence yields unsure but no justified-abstention label. Classify missing-evidence abstentions independently of survey truth, retaining unknown agreement/unsafe-pass judgments. Update fixture counts and generated results.

Confirmed at a575437 from PR #4 discussion_r4114179703. Deferred under the approved convergence rule: no source-input loss or false PASS was found.