PUBLIC-SEO-PERFORMANCE-HARDENING (SEO / Performance) & DASHBOARD-PDF-CHUNK-ISOLATION (Performance)

Release digest

PUBLIC-SEO-PERFORMANCE-HARDENING (SEO / Performance) — Added static asset cache headers, a root 404.html recovery page, trailing-slash sitemap/canonical normalization for docs and changelog surfaces, and dashboard preview-video lazy loading so PageSpeed and Google Search Console see cleaner public routes without changing product behavior.
DASHBOARD-PDF-CHUNK-ISOLATION (Performance) — Kept PDF generation dependencies out of the initial dashboard preload graph while preserving a valid production chunk graph for /app.

Added regression coverage for static cache headers, dashboard lazy media/PDF loading, docs sitemap trailing-slash policy, changelog sitemap policy, and the public noindex 404 page.
Verified dashboard, landing, knowledge-base, and changelog production builds; verified docs SEO normalization/checks; and verified /app production preview renders while loading the dashboard preview video only after user interaction.
Updated changelog and SECURITY.md freshness. Public documentation decision: no knowledge-base article is required because this is a technical SEO, static delivery, and performance hardening pass for existing public routes, not a new feature, data source, legal/security claim, pricing workflow, or user-facing product contract.