feat(canopy-seed): WIC multi-participant households (pregnant mother + infant)

Source: canopy-seed-caps-wic-fixtures plan Potential Improvements.

WIC seeder currently emits one determination per household. The most common real-world WIC enrollment is a pregnant mother + infant pair, generating two related determinations under the same household. Splitting these in seed data would exercise multi-participant rendering and the per-category food-package logic.

Acceptance: phase12_wic_determinations supports household member walks with category-aware splitting; Playwright participant tab assertions extended.