style(web): Such-Widget ohne helle Unterkante an Auswahl und Suchfeld

Opt-out-Klasse field-plain fuer die Fluent-Unterkante; im Dunkelmodus
wirkte sie im Such-Widget wie eine weisse Linie (Nutzerwunsch 29.09.).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/web/src/components/dashboard/widgets/search-widget.tsx

@@ -89,7 +89,7 @@ export function SearchWidget({ instanceId, config }: WidgetProps) {
     <div className="flex h-full items-center gap-2 px-1.5">
       {/* Provider dropdown (D-14: ~120px left) */}
       <select
-        className="h-8 w-[120px] shrink-0 rounded border border-border bg-card px-2 text-sm text-foreground"
+        className="field-plain h-8 w-[120px] shrink-0 rounded border border-border bg-card px-2 text-sm text-foreground"
         value={selectedProviderId}
         onChange={(e) => handleProviderChange(e.target.value)}
       >
@@ -103,7 +103,7 @@ export function SearchWidget({ instanceId, config }: WidgetProps) {
       {/* Search input (flex-1 center) */}
       <input
         type="text"
-        className="h-8 flex-1 rounded border border-border bg-background px-3 text-sm text-foreground placeholder:text-muted-foreground focus:outline-none focus:ring-2 focus:ring-primary"
+        className="field-plain h-8 flex-1 rounded border border-border bg-background px-3 text-sm text-foreground placeholder:text-muted-foreground focus:outline-none focus:ring-2 focus:ring-primary"
         placeholder={t('search.placeholder')}
         value={query}
         onChange={(e) => setQuery(e.target.value)}