feat(renderer): PluginsSettings tab placeholder (Coming soon)

src/renderer/components/modals/PluginsSettings.tsx

@@ -0,0 +1,14 @@
+import { Sparkles } from 'lucide-react';
+
+export function PluginsSettings() {
+  return (
+    <div className="flex flex-col items-center justify-center gap-3 py-12 text-center text-muted-foreground">
+      <Sparkles className="h-8 w-8 opacity-50" />
+      <h3 className="text-base font-semibold text-foreground">Coming soon</h3>
+      <p className="max-w-sm text-sm">
+        The plugin system is on the roadmap. You'll be able to extend MarkdownConverter with custom
+        commands, themes, and export formats.
+      </p>
+    </div>
+  );
+}