fix: improve Lighthouse performance and accessibility

[starc007]

What changed

• defer analytics and off-screen homepage previews to reduce initial work
• remove the hero subtitle animation that delayed LCP
• make popover portals hydration-safe
• prevent closed or duplicated interactive content from remaining focusable
• improve contrast, heading order, target sizes, labels, list semantics, and route metadata
• add hydration and accessibility regression coverage

Why

Lighthouse found shared accessibility issues across component pages, avoidable homepage load work, hydration recovery in portalled popovers, and several route-specific semantic issues. The local development server also exaggerates performance costs because it serves unminified Next.js development bundles, so this PR focuses on the actionable application-level findings without changing component behavior.

Validation

• bun run check
• bun test — 52 passing
• git diff --check
• Chrome verification on http://localhost:3000