feat: make API URL configurable and improve code quality

- Add configurable API URL support via environment variables
- Update nginx configuration with environment variable substitution
- Create nginx template for dynamic proxy configuration
- Update Docker configuration for environment variable handling
- Fix hardcoded localhost:8000 references in error messages
- Add proper TypeScript types for health check API
- Format all code with Prettier for consistency
- Update documentation with configuration instructions
- Improve error messages to be environment-agnostic
- Fix duplicate imports and type safety issues

BREAKING: API URL is now configurable via VITE_API_URL (dev) and API_BACKEND_URL (prod)

frontend/vite.config.ts

@@ -1,7 +1,7 @@
-import { defineConfig } from 'vite'
-import react from '@vitejs/plugin-react'
+import { defineConfig } from "vite";
+import react from "@vitejs/plugin-react";
 
 // https://vite.dev/config/
 export default defineConfig({
   plugins: [react()],
-})
+});