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/default.conf.template

@@ -0,0 +1,33 @@
+server {
+    listen 80;
+    server_name localhost;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Enable gzip compression
+    gzip on;
+    gzip_vary on;
+    gzip_min_length 1024;
+    gzip_proxied expired no-cache no-store private auth;
+    gzip_types text/plain text/css text/xml text/javascript application/javascript application/xml+rss application/json;
+
+    # Handle client-side routing
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # API proxy to backend (configurable via API_BACKEND_URL env var)
+    location /api/ {
+        proxy_pass ${API_BACKEND_URL};
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+
+    # Cache static assets
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+}