feat: use FileInput DS component for file uploads, fix certs volume perms

- Replace inline FileField and native <input type="file"> with
  FileInput from @cameleer/design-system (drag-and-drop, icons, clear)
- Update CertificatesPage and SsoPage to use FileInput + FormField
- Fix /certs volume permissions (chmod 775) so cameleer user can write

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

ui/package.json

@@ -10,7 +10,7 @@
     "postinstall": "node -e \"const fs=require('fs'),p='node_modules/@cameleer/design-system/assets/';if(fs.existsSync('public')){fs.copyFileSync(p+'cameleer3-logo.svg','public/favicon.svg')}\""
   },
   "dependencies": {
-    "@cameleer/design-system": "^0.1.42",
+    "@cameleer/design-system": "^0.0.0-snapshot.20260411.fd08d7a",
     "@logto/react": "^4.0.13",
     "@tanstack/react-query": "^5.90.0",
     "lucide-react": "^1.7.0",