fix: Auto-build before start to prevent missing .next errors

Changed `start` script to run `next build && next start` so that
cloned projects work immediately without manual build step.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "dev": "next dev",
     "build": "next build",
-    "start": "next start",
+    "start": "next build && next start",
     "lint": "next lint",
     "format": "prettier --write \"**/*.{ts,tsx,js,jsx,json,css,md}\""
   },