On phones the header spanned two rows: the title block plus a control bar of
the °F/°C toggle, bell, account and hamburger. Wrap the nav in a .nav-panel
inside the <details> menu and inject the °F/°C toggle and account/bell into that
panel instead of into the header row. On desktop the panel is display:contents,
so the inline top bar renders exactly as before (order restored via flex order);
on phones the panel becomes a right-anchored, viewport-clamped dropdown and the
header collapses to a single row (logo + name + hamburger, tagline hidden).
The viewport clamp also fixes the SEO/city pages, whose menu dropdown previously
ran off-screen.
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