[feat] improve custom icon build script with TypeScript and error handling (#5202)

- Convert customIconCollection.js to TypeScript with proper interfaces
- Add comprehensive SVG validation and error handling
- Implement graceful failure - malformed icons don't break builds
- Remove verbose logging, keep only errors/warnings
- Update documentation in README.md, CONTRIBUTING.md, icons/README.md
- Add missing @iconify/tailwind dependency

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

Co-authored-by: Claude <noreply@anthropic.com>

package-lock.json

@@ -2344,7 +2344,6 @@
       "resolved": "https://registry.npmjs.org/@iconify/tailwind/-/tailwind-1.2.0.tgz",
       "integrity": "sha512-KgpIHWOTcRYw1XcoUqyNSrmYyfLLqZYu3AmP8zdfLk0F5TqRO8YerhlvlQmGfn7rJXgPeZN569xPAJnJ53zZxA==",
       "dev": true,
-      "license": "MIT",
       "dependencies": {
         "@iconify/types": "^2.0.0"
       },