fix(index.html): change script type for env-config.js to improve compatibility

feat(env-config): add env-config.js for development environment setup

- Updated index.html to use a standard script tag for env-config.js.
- Introduced env-config.js as a development placeholder for environment variables, allowing fallback to build-time env vars.

worklenz-frontend/public/env-config.js

@@ -0,0 +1,7 @@
+// Development placeholder for env-config.js
+// In production, this file is dynamically generated with actual environment values
+// For development, we let the application fall back to import.meta.env variables
+
+// Set undefined values so the application falls back to build-time env vars
+window.VITE_API_URL = undefined;
+window.VITE_SOCKET_URL = undefined;