fix: make postinstall script cross-platform for Windows compatibility

Replace Unix-only `2>/dev/null || true` with a `node -e` inline script
that silently ignores better-sqlite3 rebuild failures on all platforms.

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

package.json

@@ -17,7 +17,7 @@
     "dev": "concurrently \"npm run dev:server\" \"vite\"",
     "dev:server": "npx tsc --watch",
     "production": "npm run build && npm run canvas",
-    "postinstall": "npm rebuild better-sqlite3 --update-binary 2>/dev/null || true",
+    "postinstall": "node -e \"const {execSync}=require('child_process');try{execSync('npm rebuild better-sqlite3 --update-binary',{stdio:'ignore'})}catch(e){}\"",
     "prepublishOnly": "npm run build",
     "setup": "node dist/index.js setup",
     "update": "node dist/index.js update",