[codex] Add healthcare compare scope

[daphnehanse11]

Summary

• Add scope=healthcare to the release comparison API and reuse the existing healthcare target predicate before computing common, added, removed, improved, and regressed targets.
• Add a Healthcare scope control on /populace/compare, URL preservation for scope, a, and b, and healthcare program cards for ACA marketplace, APTC recipients, Medicaid, Medicaid + CHIP, implied CHIP, and Medicare Part B.
• Add a healthcare target tab deep link to compare the selected release against the previous release.

Closes #53

Tests

• bun test
• bun run lint
• bun run build