Fix tablet navigation overflow

[GuanzhouSong]

Summary

Use the collapsible navigation below 1280px, where the full desktop link row does not reliably fit. Switch the desktop links, menu button, and expanded menu at the same breakpoint. Link labels, destinations, and page content are unchanged.

Previously, the desktop navigation appeared at 768px while the menu button disappeared. It made all eight sampled Next.js page types overflow: a 768px viewport had a 963px-wide document, and a 1024px viewport had a 1035px-wide document.

Validation

• Production Next.js export and TypeScript check passed in an isolated snapshot using existing dependencies and generated content (next build --webpack).
• ESLint passed for app/components/Navbar.tsx.
• Chromium passed 64 checks across eight page types at 320, 375, 768, 960, 1024, 1200, 1280, and 1440px: no horizontal overflow, with the expected navigation visible.
• Menu open, link selection, and close-on-navigation passed at 320, 768, and 1200px.
• The route/link scan of 278 exported Next.js routes is unchanged. The separate Jekyll blog layout is not affected by this change.

Manual check

Open the homepage or /docs/ at 768px and 1024px. Confirm there is no horizontal page scrolling and the menu button exposes the navigation links. At 1280px, confirm the desktop links are visible and the menu button is hidden.

Screenshots

Fresh captures of commit 9d42a0c at a 768 x 850px tablet viewport.

Menu closed	Menu open