fix(ci): skip lefthook install when .git directory missing

- Prevents lefthook from failing in CI/Vercel environments
- Only installs git hooks when in actual git repository

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

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

package.json

@@ -24,7 +24,7 @@
     "changeset": "changeset",
     "changeset:version": "changeset version && pnpm install --no-frozen-lockfile",
     "changeset:publish": "pnpm build && changeset publish",
-    "prepare": "lefthook install"
+    "prepare": "node -e \"if (require('fs').existsSync('.git')) { require('child_process').execSync('lefthook install', {stdio: 'inherit'}) }\""
   },
   "devDependencies": {
     "@biomejs/biome": "^1.9.4",