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/src/components/LoadingSpinner.tsx

@@ -1,10 +1,12 @@
-import { RefreshCw } from 'lucide-react';
+import { RefreshCw } from "lucide-react";
 
 interface LoadingSpinnerProps {
   message?: string;
 }
 
-export default function LoadingSpinner({ message = 'Loading...' }: LoadingSpinnerProps) {
+export default function LoadingSpinner({
+  message = "Loading...",
+}: LoadingSpinnerProps) {
   return (
     <div className="flex items-center justify-center p-8">
       <div className="text-center">