fix(site): stop the navbar from overflowing on mobile and tablet

[devin-ai-integration]

Summary

The navbar row was wider than the viewport at two ranges, so the whole landing (and docs) could be panned horizontally:

• < ~372px (320/360px phones): Wordmark + LangToggle + 3-button ThemeToggle + menu button didn't fit (page was 372px wide). Below sm the ThemeToggle now moves into the mobile menu as a "Theme"/"Tema" row.
• 768–~872px (tablets): the desktop row (5 links + lang + theme + GitHub) needs 849px (EN) / 872px (ES) but kicked in at md (768). The desktop links now show from lg (1024); the hamburger/mobile menu cover < lg.

Verified with Playwright: document.documentElement.scrollWidth equals the viewport at 320/360/390/414 (EN + ES, light + dark, full-page scroll, all tour tabs), at 640/768/900/1023/1024/1280 (EN + ES), and on /docs/ at 360. npm run lint and npm run build pass.

Link to Devin session: https://app.devin.ai/sessions/f2dbe552f67a42779b7c8b4302459bb2
Open in Devin Desktop: https://app.devin.ai/desktop/session/f2dbe552f67a42779b7c8b4302459bb2?variant=devin
Requested by: @Villoh

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

Retested 85f9a79 locally with touch-enabled Chrome mobile emulation: 388 runtime assertions passed, zero failures.

Tablet overflow fix verified

• EN/ES at 768px and 900px: scrollWidth == innerWidth == configured width; hamburger and GitHub fit.
• Mobile menu opens without a duplicate Theme row.
• EN/ES at 1024px and 1280px: desktop links visible, hamburger hidden, no overflow.

Phone and docs regression evidence

320/360/390px × EN/ES × light/dark passed menu/dropdown, theme-control and full-page overflow checks. Docs at 320px passed in light/dark.

Not covered: physical devices / iOS Safari.

Written by Devin