feat(cms): admin quick-search across all content (MITHOME-120)

Adds a search box to the top of every Payload admin page
(admin.components.header) that searches by text across every field of
every Global and Collection, in both locales — something Payload has
no built-in equivalent for: collection list views only search their
own title/slug fields, and Globals have no list view at all.

Implementation is deliberately client-side and index-free rather than
@payloadcms/plugin-search (a server-side search collection kept in
sync via hooks): this project's entire content is 5 Globals + 2 small
Collections, so a plugin-managed search index would be disproportionate
maintenance for the actual data volume — the same reasoning already
applied to the logo editor (MITHOME-118). On first use, the component
fetches every Global/Collection doc in both locales via the existing
REST API (same-origin, admin session cookie), recursively flattens
every field to (path, value) pairs client-side, and filters by
case-insensitive substring as the user types. Each result links
straight to the right edit view (global or collection/id).

New: src/components/admin/QuickSearch.tsx. Registered via
payload.config.ts admin.components.header, which required a
generate:importmap run — the useful gotcha this surfaced: Payload
resolves component paths against admin.importMap.baseDir, which
defaults to process.cwd() (the proto/ the CLI is run from), not
dirname(payload.config.ts) — so the path needed to be
'./src/components/admin/QuickSearch#QuickSearch', not
'./components/admin/QuickSearch#QuickSearch'. Documented inline.

Verified live in the browser (not just tsc/lint): search finds matches
in both a Global (Home hero.cta.secondary.text / services description)
and a Collection (Partners name/url), shows source + field path +
locale + a snippet per result, clicking a result navigates to the
correct edit view, and the search state persists across client-side
admin navigation since the header component doesn't remount. Zero
console errors in a fresh tab. Full gate green: tsc, lint, unit tests
(51 passed), production build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

proto/src/app/(payload)/admin/importMap.js

@@ -1,6 +1,8 @@
+import { QuickSearch as QuickSearch_899db48c9ce30e524aae8643dea53f6d } from '../../../../src/components/admin/QuickSearch'
 import { CollectionCards as CollectionCards_f9c02e79a4aed9a3924487c0cd4cafb1 } from '@payloadcms/next/rsc'
 
 /** @type import('payload').ImportMap */
 export const importMap = {
+  "./src/components/admin/QuickSearch#QuickSearch": QuickSearch_899db48c9ce30e524aae8643dea53f6d,
   "@payloadcms/next/rsc#CollectionCards": CollectionCards_f9c02e79a4aed9a3924487c0cd4cafb1
 }