chore: update unbuild 2→3

Fixes defu prototype pollution (GHSA-737v-mqg7-c878) and
esbuild vulnerability (GHSA-67mh-4wv8-2f99) in unbuild paths.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: yamatatsu

package.json

@@ -54,7 +54,7 @@
     "husky": "^9.0.11",
     "prettier": "^3.2.5",
     "typescript": "^5.4.3",
-    "unbuild": "^2.0.0",
+    "unbuild": "^3.6.1",
     "vite": "^8.0.3",
     "vitest": "^4.1.2"
   },