Evidence — navbar search shortcut affordance (/ chip + hover hints)

The search shortcuts (/ and ⌘/Ctrl+K) have always worked (assets/js/search-modal.js), but nothing in the UI advertised them — the design system's navbar (_design-system/ui_kits/website/Navbar.jsx) shows the affordance the theme lacked: a quiet <kbd>/</kbd> chip on the search button plus a shortcut hover title.

• 01-before-after.png — at 1280px and 1440px the AFTER navbar carries the / chip beside the search icon (at 1440px next to the "Search" label, exactly as in the design); BEFORE lacks it. Nav labels and layout are otherwise identical — the chip is d-xl-inline-flex so the tight 992–1199px container-query tier keeps its label budget (an earlier d-lg draft tipped that tier to icons-only; caught in this evidence run and corrected).
• 02-viewport-matrix.png — full sweep 320→1440px: no chip in mobile/tablet navbars, no overflow at any width (metrics.json: before=after=0 overflow everywhere).

Also in this change, not visible in the montage: hover titles with shortcut hints on the search button (Search — press / or Ctrl+K, swapped to ⌘K on macOS), the sidebar (b) and TOC (t) hide toggles, aria-keyshortcuts on all three, and a ⌘/Ctrl+K row in the keyboard-shortcuts modal. Regression tests: test/visual/features/search.spec.js ("opens on Cmd/Ctrl+K shortcut", "search button advertises the shortcuts").