fix: remove one-time nullifier block in v4 uniqueness verify

[Takaros999]

Summary

• Removes the one-time verification restriction for v4 uniqueness proofs in production
• Nullifier reuse is now always allowed — proofs can be verified multiple times
• Supports auditable log workflows and HITL use cases that need to re-verify the same proof

What changed

• Removed the allowNullifierReuse conditional in web/api/v4/verify/uniqueness-proof/handler.ts
• Existing nullifier now always returns 200 success instead of 400 max_verifications_reached
• Race condition on insert also returns 200 success unconditionally

Test plan

• Verify a v4 uniqueness proof in production environment
• Re-verify the same proof — should return 200 with nullifier_reused: true
• Verify staging and v3.0 paths still work as before

🤖 Generated with Claude Code

[Gr1dlock]

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[chatgpt-codex-connector]

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