receives_medicaid consumer corrections: IL BCC should read eligibility, IL FPP computed enrollment, CA freeze needs prior-year continuity

The populace#591 consumer classification (adjudication: https://github.com/PolicyEngine/populace/issues/591#issuecomment-5160668979) read all six live consumers of the reported input `receives_medicaid` against their statutory references. Three are correct as reported-coverage checks. Three should change:

1. **IL BCC — class 2 (blocking misuse)**: `il_bcc_insurance_eligible.py:26` keys on Medicaid *eligibility through another pathway* (IDHS PM 06-20-02; 305 ILCS 5/5-2), not observed receipt. Should read `person("is_medicaid_eligible", period)`. If BCC later enters general Medicaid eligibility, preserve an "otherwise eligible excluding BCC" node to avoid self-reference.
2. **IL FPP — computed substitution**: `il_fpp_eligible.py:32` — disqualifying condition is enrollment in other full medical coverage; `~person("medicaid_enrolled", period)` is the honest model and the live graph is acyclic.
3. **CA §14007.8 freeze — continuity fix**: `is_ca_medicaid_immigration_status_eligible.py:48` — the 2026 freeze grandfathers *prior enrollees*. Proposed:

```python
current_medicaid_coverage = (
person("medicaid_enrolled", period.last_year)
| person("has_medicaid_health_coverage_at_interview", period)
)
```

The prior-year chain terminates in 2025, before the freeze is active, so no recursion.

Context: populace is preparing to populate `receives_medicaid` from CPS `NOW_MCAID` (reported coverage); item 1 gates that wiring — populating the input while IL BCC misreads it as an eligibility proxy would move IL BCC results the wrong way. Full receipts at the adjudication link.

Read il_bcc_insurance_eligible.py:26, il_fpp_eligible.py:32, and is_ca_medicaid_immigration_status_eligible.py:48 alongside the linked adjudication. Update each consumer to use the stated eligibility, enrollment, or prior-year continuity logic, then verify the dependency graph remains acyclic and the three corrections match the statutory interpretations.

Written by the indexing model from the issue text.