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/index.html

@@ -13,7 +13,7 @@
   <title>Worklenz</title>
 
   <!-- Environment configuration -->
-  <script type="module" src="/env-config.js"></script>
+  <script src="/env-config.js"></script>
   <!-- Unregister service worker -->
   <script src="/unregister-sw.js"></script>
   <!-- Microsoft Clarity -->