Enforce the tier floor on verification; fix the stale refutation comment

[joshft]

Two consistency defects from external review, both verified in code before fixing:

• Evidence.Verified() accepted a passing probe at T0, which would mint StatusVerified with EffectiveTier: T0 — a verified row whose tier means "nothing checked this". The tier floor is now part of Verified() itself (the one production consumer is weigh), and a new test pins the contract: a T0 pass leaves the claim in the remainder.
• The StatusRefuted doc comment described tier-conditional dominance ("none passed at a higher tier"); weigh has always implemented unconditional refutation dominance, which is the load-bearing rule. Comment corrected.

What the receipt cannot check here: the doc-comment corrections are prose; the tier-floor change is covered by the new TestT0PassConfersNoVerification.

🤖 Generated with Claude Code

https://claude.ai/code/session_015GeUG1gboWiZSnFyzQghyp

[github-actions]

correctful receipt

13 claims — ✅ 11 verified · ❌ 0 refuted · ⚠️ 2 unverified

Change: origin/master...HEAD (6d79b77..d332508) — 3 files

⚠️ Unverified remainder (2) — what nothing checked

Claim	Statement	Source
INV-004	INV-004 (referenced; no bound probe from harvest)	schema/schema.go:113
INV-009	INV-009 (referenced; no bound probe from harvest)	schema/schema.go:154

✅ Verified (11)

Tier	Claim	Statement
T1-assertion	INV-001	Remainder Contains Every Unverified Claim
T1-assertion	INV-002	Refuted Claim Never Enters Remainder
T1-assertion	TestVerifiedClaimCarriesProbeTier	Verified Claim Carries Probe Tier
T1-assertion	INV-007	Refutation Dominates Verification
T1-assertion	TestT0PassConfersNoVerification	T0 Pass Confers No Verification
T1-assertion	TestRemainderSectionAlwaysRenders	Remainder Section Always Renders
T1-assertion	TestCoverageDisclosesUnreadFiles	Coverage Discloses Unread Files
T1-assertion	TestAnchoringSummaryAndMarkers	Anchoring Summary And Markers
T1-assertion	TestLLMProposedMarker	LLMProposed Marker
T1-assertion	TestRefutedDetailComesFromFailingProbe	Refuted Detail Comes From Failing Probe
T1-assertion	TestReceiptSanitizesPathsAndPinsSHAs	Receipt Sanitizes Paths And Pins SHAs

Harvest coverage: 3 files — 2 claimed · 1 scanned · 0 unread

_{schema 0.0.4 · exit gate: refuted claims block; the remainder informs, never fails}