fix(docs): restore search bar in starlight header (closes #2299) (#2302)

* fix(docs): restore search bar in api/guides starlight header (closes #2299)

Custom Header override replaced Starlight's default header without
re-mounting <Search />, so api.wheels.dev and guides.wheels.dev lost
the search/filter field.

Add a conditional `search` slot to the shared Header and fill it from
the Starlight override using `virtual:starlight/components/Search`,
matching the pattern already used in Footer.astro for EditLink /
LastUpdated / Pagination.

Landing/blog/packages sites are unaffected — they don't pass a search
slot, so the container is not rendered (Astro.slots.has guard).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* test(docs): refresh guides visual baseline for restored search button

Header now renders Pagefind's <Search /> button per #2299 fix. Diff
confirms only the new search button area changed (202px > 200 threshold).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bpamiri

web/packages/ui/src/components/Header.astro

@@ -23,6 +23,14 @@ const links = [
 		<slot name="after-brand" />
 	</div>
 
+	{
+		Astro.slots.has('search') && (
+			<div class="wd-header__search">
+				<slot name="search" />
+			</div>
+		)
+	}
+
 	<button
 		class="wd-header__toggle"
 		type="button"
@@ -112,6 +120,18 @@ const links = [
 		text-decoration: none;
 	}
 
+	.wd-header__search {
+		display: flex;
+		align-items: center;
+		margin-left: auto;
+		min-width: 0;
+	}
+
+	.wd-header__search :global(site-search) {
+		display: flex;
+		align-items: center;
+	}
+
 	.wd-header__nav {
 		display: flex;
 		align-items: center;

web/packages/ui/src/components/starlight/Header.astro

@@ -1,5 +1,6 @@
 ---
 import { getCollection } from 'astro:content';
+import Search from 'virtual:starlight/components/Search';
 import Header from '../Header.astro';
 import VersionSwitcher from './VersionSwitcher.astro';
 import { computeVersionOptions } from '@wheels-dev/ui/data/versions';
@@ -32,6 +33,7 @@ const currentVersion = computed?.currentVersion ?? null;
 		options={options}
 		currentVersion={currentVersion}
 	/>
+	<Search slot="search" />
 	<VersionSwitcher
 		slot="in-nav-drawer"
 		variant="drawer"