Get an aggregate sandbox institutional portfolio summary

Returns a deterministic aggregate-only sandbox portfolio summary when the authenticated automation client has portfolio.read. External URL: /v1/institutional-portfolio/current/summary. Current Next.js implementation path: /api/platform/v1/institutional-portfolio/current/summary. This read-only route does not require Idempotency-Key and never exposes exact asset or unit identifiers, addresses, tenant identity, lease terms, rent or valuation amounts, vendor details, investor reports, source exports, credentials, write controls, or live portfolio integrations. Professional and data review remain required; all portfolio, lease, maintenance, capex, compliance, reporting, and export actions are explicitly deferred.