Reproduce-in-Python still generates archived policyengine-us-data URIs; should emit the populace default

[MaxGhenis]

The live "Reproduce in Python" feature still generates code pointing at the archived policyengine-us-data HF repo: src/data/reformDefinitionCode.js (and its test) hardcode hf://policyengine/policyengine-us-data/..., so users copying reproduction snippets from policyengine.org are directed at the deprecated dataset instead of the populace default that policyengine.py actually resolves (hf://policyengine/populace-us/populace_us_2024.h5 at the pinned certified revision).

Found during the populace#204 artifact-replacement audit (full table: PolicyEngine/microcosm#204 (comment)). The prior tracking issue (#2828) was closed as "moved to policyengine-app-v2" (#1079 covers v2), but v1 — the production frontend — was never re-filed.

Scope: the code generator + test only. Historical blog posts referencing the old repo are covered separately (#2659).

[MaxGhenis]

Closing as part of the policyengine-app (v1) wind-down: policyengine.org is now served by policyengine-app-v2, and this repository is being archived. This issue's body already notes that the archived-URI problem is tracked for v2; the v2 equivalent is policyengine-app-v2#1079, with the fix landed in policyengine-app-v2#1090. Following up there.