redesign search dialog (no accent ring, cleaner rows)

[Flotapponnier]

Summary

Follow-up to #680 — commit landed after the merge. Cleans up the search dialog itself (the modal that opens on click / Cmd+K) which the previous PRs left untouched.

Fixes

• Orange focus ring removed: the global `input:focus-visible { outline: 2px solid accent }` rule was reading as a validation error on the cmdk input. `[cmdk-input]` now opts out of the universal ring (rest of the site still gets it).
• `{{best_name}}` in search descriptions: build-time index had no Prom data to resolve templates, so descriptions like "{{best_name}} leads ..." shipped raw. Now fall back to `spec.subtitle` when `seo_description` contains `{{` tokens.

Redesign

• Wider modal (`max-w-2xl` vs `max-w-xl`), softer border, deeper shadow.
• Backdrop blur bumped (`backdrop-blur-md`).
• Item rows: dropped the bordered "BENCHMARK" pill, replaced with small uppercase kind label + middle-dot + title, plus an ArrowRight that lights up on the selected row.
• Footer with kbd hints (↑↓ navigate, ↵ open, esc close) replacing the cramped microcaps.

Test plan

• Open dialog (Cmd+K) → no orange ring on the input.
• Empty query → "Popular benchmarks" group renders with clean rows.
• Type "rpc" → no `{{best_name}}` in any description.
• Arrow up/down + enter navigates correctly; esc closes.