Description

During PDF/browser export, every slide is rendered at once under /export. PrintSlideClick already provides a fixed navigation context for each rendered slide, but the public useNav() composable always returned the application-wide shared nav instead. Components such as slide-top.vue therefore saw the route-level slide number (typically 1) on every exported page, and tocTree.active stayed fixed as well.

This change keeps the existing shared nav as the global source of router/print state, then overlays the nearest slide-local nav when a rendered slide provides one. Normal play/presenter views continue to receive the same shared nav object; export children receive their fixed currentSlideNo, currentSlideRoute, clicks, and TOC state while retaining the full nav API.

Tests

Added an SSR regression test that renders a child component under a slide-local export context while the global export route points at slide 1. It verifies that useNav() returns slide 2, its frontmatter, and the slide-2 active TOC entry.

• pnpm exec vitest run packages/client — 5 passed
• pnpm typecheck
• targeted ESLint for the changed files
• pnpm build

Closes #2670