fix(perf): require usable repeat references and complete metric observations - #22

Closes #14. Builds on the descriptive ranges/--reference support from PR #10.

A supplied reference can no longer silently vanish from qualification. Reference-aware changes and drift require complete eligible reference evidence, matched ordered completion counts and complete matching baseline declarations. The output exposes reference model/deployment and declared-match/mismatch/unavailable status; matching declarations do not verify physical restoration or a causal A/B/A experiment. Ineligible/missing evidence stays inspectable with explicit reasons and an ineligible exit, not an automatic two-run fallback.

Reference-aware stream metrics also require all paired lane observations across A/B/A2; a few surviving prefill lanes cannot silently replace the full metric. Other available metrics and the ordinary no-reference path retain their scope. Comparison JSON advances to version 3 for the changed reference eligibility contract. Old execution receipts remain readable and unchanged.

Proposal reconciliation: retained min/max ranges and pooled reference ranges are a coarse descriptive filter. This does not add bootstrap confidence intervals, within_noise significance or the proposed absolute-drift threshold. Those require a separate validated statistical design; observed range separation does not certify significance or equality.

Verified: independent SIX/HELP reviews (both initially blocked partial lane dropout; both approved its fix), exact-head fmt/Clippy/workspace tests/release build; regression failed before the dropout fix and passed afterward; loopback CLI tested valid and undeclared repeat behavior, saved pre-change runs remain readable. No real A/B/A inference run or server restoration verification was performed.