Model New Mexico Puente Health premium backfill for lawfully-present non-citizens (esp. PY2027 ≤400% FPL)

### Summary
New Mexico's **Puente Health** program backfills state premium assistance for lawfully-present non-citizens who lose the federal PTC under P.L. 119-21. It is not modeled, and PolicyEngine's own gates zero out the population Puente covers — so the model currently shows these New Mexicans losing all assistance while 8.401.2.11 NMAC actually backfills them through the NMPA machinery.

### Details
- Puente began 2026-01-01 (<100% FPL) and **expands to ≤400% FPL for PY2027** (PY2027 MAP Policy & Procedures Manual, HCA 2026-06-16, pp. 2, 7–8).
- It pays through the NMPA machinery on Table 1; PY2027 MAP eligibility item 2 (p. 4) admits Puente enrollees to NMPA by name.
- PolicyEngine already encodes the federal-side losses (`below_fpl_immigration_exception_in_effect` false in 2026; `ineligible_immigration_statuses` 2027 restriction), so the model shows this population losing everything.

**Bias:** understates NM state benefits for lawfully-present non-citizens — a small slice in 2026, but the whole ≤400% FPL lawfully-present-non-citizen marketplace population in 2027.

### Scope
Surfaced in the review of the NM Premium Assistance PR (#9232); documented there as Not-Modeled. This issue tracks implementing the Puente backfill (8.401.2.11 NMAC). Note the §73101 (manual) vs §71301 (repo parameter) citation discrepancy to reconcile when implementing.

_Filed per review item A6 (reviewer @hua7450)._

Start by reviewing the NM Premium Assistance PR #9232 and the existing federal gates, especially below_fpl_immigration_exception_in_effect and ineligible_immigration_statuses. Trace the NMPA machinery and reconcile the §73101 versus §71301 citation. Done means Puente backfill is represented from 2026-01-01 and expands to lawfully-present non-citizens at or below 400% FPL for PY2027.

Written by the indexing model from the issue text.