feat: add serve command for landing page preview

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

package.json

@@ -10,6 +10,7 @@
     "build": "bash scripts/build.sh",
     "build:demo": "slidev build decks/demo/slides.md --base /demo/ --out dist/demo",
     "build:showcase": "slidev build decks/showcase/slides.md --base /showcase/ --out dist/showcase",
+    "serve": "pnpm run build && pnpm exec serve dist -l 3030",
     "export": "slidev export"
   },
   "keywords": [],
@@ -25,6 +26,7 @@
   "type": "module",
   "devDependencies": {
     "@slidev/cli": "^52.15.2",
-    "@slidev/theme-default": "^0.25.0"
+    "@slidev/theme-default": "^0.25.0",
+    "serve": "^14.2.6"
   }
 }