Fix remaining state CDCC defects from the § 21 coupling audit (WI/NY/HI gating, WI rate vintage, AR refundability, VT 2022)

Split from the #8826 audit (completed in #8933), which verified every state CDCC/§21 consumer against its conformity statute and fixed the OBBBA-vintage and §129 drift. These remaining defects were confirmed during that audit but deliberately left out of its lane:

1. **WI/NY/HI filing-status gating**: these states' CDCC variables do not route through the shared `cdcc_filing_status_eligible` gate, so the § 21(e)(2) joint-return requirement and § 21(e)(4) separated-taxpayer exception are mis-applied (SC was fixed the same way in #8933 — same pattern applies).
2. **WI rate drift (2024+ branch)**: `wi_childcare_expense_credit_potential` reads `cdcc_rate` directly, embedding the 2026 OBBBA rate schedule, while Wisconsin conforms statically to the IRC as of **Dec 31, 2022** (Wis. Stat. §§ 71.01/71.22). It should compute from the pre-OBBBA rate (the `pre_obbba_cdcc*` pattern from #8933), and — being pinned to 2022 — arguably from the pre-2026 schedule generally. Fix together with item 1's WI gating change.
3. **AR refundability**: flagged in the #8826 verification comment — check `ar_cdcc` refundable/non-refundable treatment against Ark. Code § 26-51-502.
4. **VT TY2022 value**: flagged in the same comment — verify the Vermont credit percentage/coupling for tax year 2022 against 32 V.S.A. § 5828c as then in effect.
5. **Expense-base under-inclusion**: the audit noted the shared federal expense base may under-include some § 21(b)(2) employment-related expenses; scope precisely before changing.

Conformity research (statutes, dates, and per-state coupling table) is recorded in #8933's PR body for reuse.

Start with the #8933 PR body and the shared cdcc_filing_status_eligible gate, then inspect the named WI, NY, HI, AR, and VT CDCC variables, including wi_childcare_expense_credit_potential and ar_cdcc. Compare each behavior with the cited statutes and conformity dates; done means the gating, WI rate vintage, AR refundability, VT 2022 value, and any precisely scoped expense-base issue are verified or corrected.

Written by the indexing model from the issue text.