Clean up client.js imports, extract GA tracking ID to env variable, and document env setup in README
- Reorganize imports into logical groups (base libs, routing, i18n, forms, grid, UI, utils)
- Consolidate two separate export blocks into one
- Fix "responsed" typo in 302 error message
- Simplify validResponse, response interceptor, and error message handling
- Extract renderApp() helper to deduplicate bootstrap rendering
- Move GA tracking ID to env variable with .env file, webpack DefinePlugin, and conditional init
- Add .env to .gitignore
- Document environment variables setup in README