feat: real data for 7 case_detail stub sections (persons, assets, expenses, verifications, audit, cross_program, documents)

Stub sections shipped in Stage 5 MR4b (#497 (closed)) as "coming soon" placeholders. Wire real data per-section.

Sections: persons, assets, expenses, verifications, audit, cross_program, documents.

Per-section work: identify backend service + endpoint, design Askama template + RenderedSection finalize wrapper, swap placeholder partial for real fetch.

Tracking origin: Stage 5 MR4b stub-shipping. Refs &51.