fix(search): align DocSearch v4 modal colors with the Playwright brand

[Skn0tt]

Summary

After the Docusaurus migration bumped Algolia DocSearch from v3 to v4, the search modal stopped picking up our brand color. DocSearch v4 moved its accent onto new CSS variables (--docsearch-highlight-color and friends) that Docusaurus's theme-search-algolia doesn't map to Infima — so on our green-branded site they fall back to Algolia blue/indigo, and dark mode renders navy surfaces.

This overrides the unmapped DocSearch v4 variables in custom.css so the search modal uses the Playwright green accent and neutral surfaces in both light and dark themes. Per DocSearch's styling docs, overriding these variables is the intended customization path for brand-colored sites.

What changed

• Accent: magnifier, search/back icons, match highlights, links, and the selected-result row now use Playwright green instead of Algolia blue.
• Dark surfaces: modal / result / background surfaces go from navy-indigo to neutral Playwright dark (#242526 / #1b1b1d).
• Neutral greys: indigo-tinted secondary text / icon / subtle colors neutralized.
• "No results" icon: its inline SVG hardcodes stroke="#5a5e9a" and ignores the variable palette, so it's neutralized with an explicit CSS rule.
• Algolia logo intentionally left blue — its SVG uses hardcoded fills and the free tier requires the mark to stay unmodified.

Before / After

Light mode

Before	After

Dark mode

Before	After

"No results" icon

Before	After

Notes

• Scoped to src/css/custom.css; no config or dependency changes.
• Verified by inspecting the live computed --docsearch-* values in both themes on the running dev server.