feat(search): add search syntax help tooltip

apps/web/src/features/search/components/search-page/SearchPageHeader.tsx

@@ -3,6 +3,7 @@ import { Search, X } from 'lucide-react';
 import { useDebounce } from '@/hooks/useDebounce';
 import { searchApi } from '@/services/api/search';
 import { SearchResults } from '@/types/search';
+import { HelpText } from '@/components/ui/HelpText';
 
 interface SearchPageHeaderProps {
   query: string;
@@ -104,6 +105,11 @@ export function SearchPageHeader({
               aria-haspopup="listbox"
               role="combobox"
             />
+            <HelpText
+              text='Utilisez AND, OR, NOT et "phrase exacte" pour affiner votre recherche.'
+              position="bottom"
+              className="mr-2"
+            />
             {query && (
               <button
                 type="button"