fix(plugin-market): keep fixed card width regardless of result count

The result grid used auto-fit tracks, so a single search result stretched
to fill the whole row. Switch to fixed responsive column counts (1/2/3/4
across breakpoints), matching langbot-space, so cards keep a consistent
max width no matter how many results are shown.

web/src/app/home/plugins/components/plugin-market/PluginMarketComponent.tsx

@@ -858,7 +858,7 @@ function MarketPageContent({
           </div>
         ) : (
           <>
-            <div className="grid grid-cols-[repeat(auto-fit,minmax(min(100%,22rem),1fr))] gap-6 mt-6">
+            <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 2xl:grid-cols-4 gap-6 mt-6">
               {visiblePlugins.map((plugin) => (
                 <PluginMarketCardComponent
                   key={plugin.pluginId}