Dashboard: Overview above-the-fold load (API split + deferred sections)

[unjica]

Summary

Overview first paint is dominated by a single /api/overview payload that feeds ATF (health, KPIs) and below-the-fold sections (trends, breakdowns, tables). Split the API (and page) so ATF loads first; defer heavier sections after paint (same trigger model as list-page ATF work — not scroll-gated).

Why later

Depends on API contract changes; list pages can ship ATF-first first using existing endpoints.

Approach (high level)

• Define an ATF overview response (greeting/health/KPIs/range meta) vs deferred sections (series, top groups, tables, extra charts)
• Parallel-fetch ATF on SSR; client-fetch deferred slices after paint
• Avoid breaking current overview URL/query contracts; version or additive endpoints preferred

Deliverables

• API: split or additive endpoints for ATF vs deferred overview data
• Dashboard: ATF SSR + deferred section loading with skeletons
• Docs / changelog for API consumers if public surface changes
• Tests for new/changed overview handlers

Depends on / precedes

Ship list-page ATF-first work first (linked).

Base branch

develop

[unjica]

Ship list-page ATF first: #486