fix: postinstall creates public/ dir before copying favicon

Docker build copies package.json before source, so public/ doesn't
exist when npm ci runs postinstall. Use mkdirSync(recursive:true).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/package.json

@@ -12,7 +12,7 @@
     "preview": "vite preview",
     "generate-api": "openapi-typescript src/api/openapi.json -o src/api/schema.d.ts",
     "generate-api:live": "curl -s http://localhost:8081/api/v1/api-docs -o src/api/openapi.json && openapi-typescript src/api/openapi.json -o src/api/schema.d.ts",
-    "postinstall": "node -e \"require('fs').copyFileSync('node_modules/@cameleer/design-system/assets/cameleer3-logo.svg','public/favicon.svg')\""
+    "postinstall": "node -e \"const fs=require('fs');fs.mkdirSync('public',{recursive:true});fs.copyFileSync('node_modules/@cameleer/design-system/assets/cameleer3-logo.svg','public/favicon.svg')\""
   },
   "dependencies": {
     "@cameleer/design-system": "^0.1.37",